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中英文对照外文翻译(文档含英文原文和中文翻译)Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application.Once installed on a device, each Android application lives in its own security sandbox:The Android operating system is a multi-user Linux system in which each application is a different user.By default, the system assigns each application a unique Linux user ID (the ID is used only by the system and is unknown to the application). The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.Each process has its own virtual machine (VM), so an application's code runs in isolation from other applications.By default, every application runs in its own Linux process. Android starts the process when any of the application's components need to be executed, then shuts down the process when it's no longer needed or when the system must recover memory for other applications. In this way, the Android system implements the principle of least privilege. That is, each application, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an application cannot access parts of the system for which it is not given permission.However, there are ways for an application to share data with other applications and for an application to access system services:It's possible to arrange for two applications to share the same Linux user ID, in which case they are able to access each other's files. To conserve system resources, applications with the same user ID can also arrange to run in the same Linux process and share the same VM (the applications must also be signed with the same certificate).An application can request permission to access device data such as the user's contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. All application permissions must be granted by the user at install time.That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to:1、The core framework components that define your application.2、The manifest file in which you declare components and required device features for your application.3、Resources that are separate from the application code and allow your application to gracefully optimize its behavior for a variety of device configurations.Application ComponentsApplication components are the essential building blocks of an Android application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each oneexists as its own entity and plays a specific role—each one is a unique building block that helps define your application's overall behavior.There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.Here are the four types of application components:ActivitiesAn activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. As such, a different application can start any one of these activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture.An activity is implemented as a subclass of Activity and you can learn more about it in the Activities developer guide.ServicesA service is a component that runs in the background to perform long-running operations or to perform work for remote processes. A service does not provide a user interface. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. Another component, such as an activity, can start the service and let it run or bind to it in order to interact with it.A service is implemented as a subclass of Service and you can learn more about it in the Services developer guide.Content providersA content provider manages a shared set of application data. You can store the data in the file system, an SQLite database, on the web, or any other persistent storage location your application can access. Through the content provider, other applications can query or evenmodify the data (if the content provider allows it). For example, the Android system provides a content provider that manages the user's contact information. As such, any application with the proper permissions can query part of the content provider (such as ContactsContract.Data) to read and write information about a particular person.Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the Note Pad sample application uses a content provider to save notes.A content provider is implemented as a subclass of ContentProvider and must implement a standard set of APIs that enable other applications to perform transactions. For more information, see the Content Providers developer guide.Broadcast receiversA broadcast receiver is a component that responds to system-wide broadcast announcements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service to perform some work based on the event.A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. For more information, see the BroadcastReceiver class.A unique aspect of the Android system design is that any application can start another application’s component. For example, if you want the user to capture a photo with the device camera, there's probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You don't need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application.When the system starts a component, it starts the process for that application (if it's not already running) and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your application's process. Therefore, unlike applications on most other systems, Android applications don't have a single entry point (there's no main()function, for example).Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies your intent to start a particular component. The system then activates the component for you.Activating ComponentsThree of the four component types—activities, services, and broadcast receivers—are activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another.An intent is created with an Intent object, which defines a message to activate either a specific component or a specific type of component—an intent can be either explicit or implicit, respectively.For activities and services, an intent defines the action to perform (for example, to "view" or "send" something) and may specify the URI of the data to act on (among other things that the component being started might need to know). For example, an intent might convey a request for an activity to show an image or to open a web page. In some cases, you can start an activity to receive a result, in which case, the activity also returns the result in an Intent (for example, you can issue an intent to let the user pick a personal contact and have it returned to you—the return intent includes a URI pointing to the chosen contact).For broadcast receivers, the intent simply defines the announcement being broadcast (for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low").The other component type, content provider, is not activated by intents. Rather, it is activated when targeted by a request from a ContentResolver. T he content resolver handles all direct transactions with the content provider so that the component that's performing transactions with the provider doesn't need to and instead calls methods onthe ContentResolver object. This leaves a layer of abstraction between the content provider and the component requesting information (for security).There are separate methods for activating each type of component:You can start an activity (or give it something new to do) by passingan Intent to startActivity() or startActivityForResult() (when you want the activity to return a result).You can start a service (or give new instructions to an ongoing service) by passingan Intent to startService(). Or you can bind to the service by passing an Intent to bindService().You can initiate a broadcast by passing an Intent to methodslike sendBroadcast(), sendOrderedBroadcast(), or sendStickyBroadcast().You can perform a query to a content provider by calling query() on a ContentResolver.For more information about using intents, see the Intents and Intent Filters document. More information about activating specific components is also provided in the following documents: Activities, Services, BroadcastReceiver and Content Providers.Declaring componentsThe primary task of the manifest is to inform the system about the application's components. For example, a manifest file can declare an activity as follows:In the <application> element, the android:icon attribute points to resources for an icon that identifies the application.In the <activity> element, the android:name at tribute specifies the fu lly qualified class name of the Activity subclass and the android:label attributes specifies a string to use as the user-visible label for the activity.You must declare all application components this way:1、<activity>elements for activities2、<service> elements for services3、<receiver>elements for broadcast receivers4、<provider>elements for content providersActivities, services, and content providers that you include in your source but do not declare in the manifest are not visible to the system and, consequently, can never run. However, broadcast receivers can be either declared in the manifest or created dynamically in code (as BroadcastReceiver objects) and registered with the system bycalling registerReceiver().Declaring component capabilitiesAs discussed above, in Activating Components, you can use an Intent to start activities, services, and broadcast receivers. You can do so by explicitly naming the target component (using the component class name) in the intent. However, the real power of intents lies in the concept of intent actions. With intent actions, you simply describe the type of action you want to perform (and optionally, the data upon which you’d like to perform the action) and allow the system to find a component on the device that can perform the action and start it. If there are multiple components that can perform the action described by the intent, then the user selects which one to use.The way the system identifies the components that can respond to an intent is by comparing the intent received to the intent filters provided in the manifest file of other applications on the device.When you declare a component in your application's manifest, you can optionally include intent filters that declare the capabilities of the component so it can respond to intents from other applications. You can declare an intent filter for your component by addingan <intent-filter>element as a child of the component's declaration element.For example, an email application with an activity for composing a new email might declare an intent filter in its manifest entry to respond to "send" intents (in order to send email). An activity in your application can then create an intent with the “send” action (ACTION_SEND), which the system matches to the email application’s “send” activity and launches it when you invoke the intent with startActivity().For more about creating intent filters, see the Intents and Intent Filters document.Declaring application requirementsThere are a variety of devices powered by Android and not all of them provide the same features and capabilities. In order to prevent your application from being installed on devices that lack features needed by your application, it's important that you clearly define a profile for the types of devices your application supports by declaring device and software requirements in your manifest file. Most of these declarations are informational only and the system does not read them, but external services such as Google Play do read them in order to provide filtering for users when they search for applications from their device.For example, if your application requires a camera and uses APIs introduced in Android 2.1 (API Level7), you should declare these as requirements in your manifest file. That way, devices that do not have a camera and have an Android version lower than 2.1 cannot install your application from Google Play.However, you can also declare that your application uses the camera, but doesnot require it. In that case, your application must perform a check at runtime to determine if the device has a camera and disable any features that use the camera if one is not available.Here are some of the important device characteristics that you should consider as you design and develop your application:Screen size and densityIn order to categorize devices by their screen type, Android defines two characteristics for each device: screen size (the physical dimensions of the screen) and screen density (the physical density of the pixels on the screen, or dpi—dots per inch). To simplify all the different types of screen configurations, the Android system generalizes them into select groups that make them easier to target.The screen sizes are: small, normal, large, and extra large.The screen densities are: low density, medium density, high density, and extra high density.By default, your application is compatible with all screen sizes and densities, because the Android system makes the appropriate adjustments to your UI layout and image resources. However, you should create specialized layouts for certain screen sizes and provide specialized images for certain densities, using alternative layout resources, and by declaring in your manifest exactly which screen sizes your application supports withthe <supports-screens> element.For more information, see the Supporting Multiple Screens document.Input configurationsMany devices provide a different type of user input mechanism, such as a hardware keyboard, a trackball, or a five-way navigation pad. If your application requires a particular kind of input hardware, then you should declare it in your manifest with the <uses-configuration> element. However, it is rare that an application should require a certain input configuration.Device featuresThere are many hardware and software features that may or may not exist on a given Android-powered device, such as a camera, a light sensor, bluetooth, a certain version of OpenGL, or the fidelity of the touchscreen. You should never assume that a certain feature is available on all Android-powered devices (other than the availability of the standard Android library), so you should declare any features used by your application withthe <uses-feature> element.Platform VersionDifferent Android-powered devices often run different versions of the Android platform, such as Android 1.6 or Android 2.3. Each successive version often includes additional APIs not available in the previous version. In order to indicate which set of APIs are available, each platform version specifies an API Level (for example, Android 1.0 is API Level 1 and Android 2.3 is API Level 9). If you use any APIs that were added to the platform after version 1.0, you should declare the minimum API Level in which those APIs were introduced using the <uses-sdk> element.It's important that you declare all such requirements for your application, because, when you distribute your application on Google Play, the store uses these declarations to filter which applications are available on each device. As such, your application should be available only to devices that meet all your application requirements.For more information about how Google Play filters applications based on these (and other) requirements, see the Filters on Google Play document.Application ResourcesAn Android application is composed of more than just code—it requires resources that are separate from the source code, such as images, audio files, and anything relating to the visual presentation of the application. For example, you should define animations, menus, styles, colors, and the layout of activity user interfaces with XML files. Using application resources makes it easy to update various characteristics of your application without modifying code and—by providing sets of alternative resources—enables you to optimize your application for a variety of device configurations (such as different languages and screen sizes).For every resource that you include in your Android project, the SDK build tools define a unique integer ID, which you can use to reference the resource from your application code or from other resources defined in XML. For example, if your application c ontains an image file named logo.png (saved in the res/drawable/ directory), the SDK tools generate a resource IDnamed R.drawable.logo, which you can use to reference the image and insert it in your user interface.One of the most important aspects of providing resources separate from your source code is the ability for you to provide alternative resources for different device configurations. For example, by defining UI strings in XML, you can translate the strings into other languages and save those strings in separate files. Then, based on a language qualifier that you append to the resource directory's name (such as res/values-fr/ for French string values) and the user's language setting, the Android system applies the appropriate language strings to your UI.Android supports many different qualifiers for your alternative resources. The qualifier is a short string that you include in the name of your resource directories in order to define the device configuration for which those resources should be used. As another example, you should often create different layouts for your activities, depending on the device's screen orientation and size. For example, when the device screen is in portrait orientation (tall), you might want a layout with buttons to be vertical, but when the screen is in landscape orientation (wide), the buttons should be aligned horizontally. To change the layout depending on the orientation, you can define two different layouts and apply the appropriate qualifier to each layout's directory name. Then, the system automatically applies the appropriate layout depending on the current device orientation.For more about the different kinds of resources you can include in your application and how to create alternative resources for various device configurations, see theApplication Resources developer guide.安卓应用基础在Java编程语言编写的Android应用程序的Android的SDK工具编译代码以及与任何数据和到一个Android的包，一个归档文件档案资源的.apk后缀，所有的在一个单一的代码.apk文件被认为是一个应用程序，是Android的文件，供电设备来安装应用程序。

Application FundamentalsAndroid applications are written in the Java programming language. The compiled Java code —along with any data and resource files required by the application —is bundled by the aapt tool into an Android package, an archive file marked by an .apk suffix. This file is the vehicle for distributing the application and installing it on mobile devices; it's the file users download to their devices. All the code in a single .apk file is considered to be one application.Android应用基础：Android应用程序是通过java语言开发的，通过绑定一些应用所需要的东西，例如：编译的Java代码，加上数据和一些资源文件，使用一个apt的工具将所有的东西封装成一个android包，这个文件的文件后缀是.apk。

这个文件是分发并安装应用程序到移动设备的载体，是用户获得该应用程序所需要的下载的文件。

Application Components A central feature of Android is that one application can make use of elements of other applications (provided those applications permit it). For example, if your application needs to display a scrolling list of images and another application has developed a suitable scroller and made it available to others, you can call upon that scroller to do the work, rather than develop your own. Your application doesn't incorporate the code of the other application or link to it. Rather, it simply starts up that piece of the other application when the need arises. For this to work, the system must be able to start an application process when any part of it is needed, and instantiate the Java objects for that part. Therefore, unlike applications on most other systems, Android applications don't have a single entry point for everything in the application (no main() function, for example). Rather, they have essential components that the system can instantiate and run as needed. There are four types of components:Activities An activity presents a visual user interface for one focused endeavor the user can undertake. For example, an activity might present a list of menu items users can choose from or it might display photographs along with their captions. A text messaging application might have one activity that shows a list of contacts to send messages to, a second activity to write the message to the chosen contact, and other activities to review old messages or changesettings. Though they work together to form a cohesive user interface, each activity is independent of the others. Each one is implemented as a subclass of the Activity base class. An application might consist of just one activity or, like the text messaging application just mentioned, it may contain several. What the activities are, and how many there are depends, of course, on the application and its design. Typically, one of the activities is marked as the first one that should be presented to the user when the application is launched. Moving from one activity to another is accomplished by having the current activity start the next one. Android有四大应用程序组件Android的一个很重要的中心特征就是一个应用程序能充分利用其他的应用程序的一些组件（前提是被允许的）例如：如果的当前开发的应用需要一个滚动的列表去展示相片并且当时其他的程序已经开发了一个合适的滚动列表并且对其他人可用，你可以调用这个滚动的列表来完成你的工作而不是开发你自己的。

Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDK tools compile the code-along with any data and resource files—into an Android package，an archive file with an .apk suffix。

All the code in a single 。

apk file is considered to be one application and is the file that Android—powered devices use to install the application.Once installed on a device，each Android application lives in its own security sandbox:The Android operating system is a multi-user Linux system in which each application is a different user.By default，the system assigns each application a unique Linux user ID （the ID is used only by the system and is unknown to the application）。

The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.Each process has its own virtual machine （VM），so an application's code runs in isolation from other applications。

Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with . All the code in a is considered to be one application and is the file that Android-powered devices use to install the application.Once installed on a device, each Android application lives in its own security sandbox:The Android operating system is a multi-user Linux system in which each application is a different user.By default, the system assigns each application a unique Linux user ID the ID is used only by the system and is unknown to the application. The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.Each process has its own virtual machine VM, so an application's code runs in isolation from other applications.By default, every application runs in its own Linux process. Android starts the process when any of the application's components need to be executed, then shuts down the process when it's no longer needed or when the system must recover memory for other applications.In this way, the Android system implements the principle of least privilege. That is, each application, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an application cannot access parts of the system for which it is not given permission.However, there are ways for an application to share data with other applications and for an application to access system services:It's possible to arrange for two applications to share the same Linux user ID, in which case they are able to access each other's files. To conserve system resources, applications with the same user ID can also arrange to run in the same Linux process and share the same VM the applications must also be signed with the same certificate.An application can request permission to access device data such as the user's contacts, SMS messages, the mountable storage SD card, camera, Bluetooth, and more. All application permissions must be granted by the user at install time.That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to:1、The core framework components that define your application.2、The manifest file in which you declare components and required device features for your application.3、Resources that are separate from the application code and allow your application to gracefully optimize its behavior for a variety of device configurations.Application ComponentsApplication components are the essential building blocks of an Android application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each one exists as its own entity and plays a specific role—each one is a unique building block that helps define your application's overall behavior.There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.Here are the four types of application components:ActivitiesAn activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. As such, a different application can start any one of these activities if the email application allows it. For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture.An activity is implemented as a subclass ofand you can learn more about it in thedeveloper guide.ServicesA service is a component that runs in the background to perform long-running operations or to perform work for remote processes. A service does not provide a user interface. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. Another component, such as an activity, can start the service and let it run or bind to it in order to interact with it.A service is implemented as a subclass of and you can learn more about it in thedeveloper guide.Content providersA content provider manages a shared set of application data. You can store the data in the file system, an SQLite database, on the web, or any other persistent storage location your application can access. Through the content provider, other applications can query or even modify the data if the content provider allows it. For example, the Android system provides a content provider that manages the user's contact information. As such, anyapplication with the proper permissions can query part of the content provider such as to read and write information about a particular person.Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the sample application uses a content provider to save notes.A content provider is implemented as a subclass ofand must implement a standard set of APIs that enable other applications to perform transactions. For more information, see the developer guide.Broadcast receiversAbroadcast receiveris a component that responds to system-wide broadcast announcements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they mayto alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service to perform some work based on the event.A broadcast receiver is implemented as a subclass of and each broadcast is delivered as an object. For more information, see the class.A unique aspect of the Android system design is that any application can start another application’s component. For example, if you want the user to capture a photo with the device camera, there's probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You don't need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures a photo. Whencomplete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application.When the system starts a component, it starts the process for that application if it's not already running and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your application's process. Therefore, unlike applications on most other systems, Android applications don't have a single entry point there's nomainfunction, for example.Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies your intent to start a particular component. The system then activates the component for you.Activating ComponentsThree of the four component types—activities, services, and broadcast receivers—are activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime you can think of them as the messengers that request an action from other components, whether the component belongs to your application or another.An intent is created with an object, which defines a message to activate either a specific component or a specific type of component—an intent can be either explicit or implicit, respectively.For activities and services, an intent defines the action to perform for example, to "view" or "send" something and may specify the URI of the data to act on among other things that the component being started might need to know. For example, an intent might convey a request for an activity to show an image or to open a web page. In some cases, you can start an activity to receive a result, in which case, the activity also returns the result in anfor example, you can issue an intent to let the user pick a personal contactand have it returned to you—the return intent includes a URI pointing to the chosen contact.For broadcast receivers, the intent simply defines the announcement being broadcast for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low".The other component type, content provider, is not activated by intents. Rather, it is activated when targeted by a request from a. T he content resolver handles all direct transactions with the content provider so that the component that's performing transactions with the provider doesn't need to and instead calls methods on the object. This leaves a layer of abstraction between the content provider and the component requesting information for security.There are separate methods for activating each type of component:You can start an activity or give it something new to do by passing antoorwhen you want the activity to return a result.You can start a service or give new instructions to an ongoing service by passing anto. Or you can bind to the service by passing an to.You can initiate a broadcast by passing anto methods like,, or.You can perform a query to a content provider by calling on a.For more information about using intents, see the document. More information about activating specific components is also provided in the following documents:,,and.Declaring componentsThe primary task of the manifest is to inform the system about the application's components. For example, a manifest file can declare an activity as follows:In the element, the android:icon attribute points to resources for an icon that identifies the application.In theelement, theandroid:name at tribute specifies the fu lly qualified class name of the subclass and theandroid:label attributes specifies a string to use as the user-visible label for the activity.You must declare all application components this way:1、elements for activities2、elements for services3、elements for broadcast receivers4、elements for content providersActivities, services, and content providers that you include in your source but do not declare in the manifest are not visible to the system and, consequently, can never run. However, broadcast receivers can be either declared in the manifest or created dynamically in code as objects and registered with the system by calling.Declaring component capabilitiesAs discussed above, in, you can use anto start activities, services, and broadcast receivers. You can do so by explicitly naming the target component using the component class name in the intent. However, the real power of intents lies in the concept of intent actions. With intent actions, you simply describe the type of action you want to perform and optionally, the data upon which you’d like to perform the action and allow the system to find a component on the device that can perform the action and start it. If there are multiple components that can perform the action described by the intent, then the user selects which one to use.The way the system identifies the components that can respond to an intent is by comparing the intent received to the intent filters provided in the manifest file of other applications on the device.When you declare a component in your application's manifest, you can optionally include intent filters that declare the capabilities of the component so it can respond to intents from other applications. You can declare an intent filter for your component by adding an element as a child of the component's declaration element.For example, an email application with an activity for composing a new email might declare an intent filter in its manifest entry to respond to "send" intents in order to send email. An activity in your application can then create an intent with the “send” action, which the system matches to the email application’s “send” activity and launches it when you invoke the intent with.For more about creating intent filters, see thedocument.Declaring application requirementsThere are a variety of devices powered by Android and not all of them provide the same features and capabilities. In order to prevent your application from being installed on devices that lack features needed by your application, it's important that you clearly define a profile for the types of devices your application supports by declaring device and software requirements in your manifest file. Most of these declarations are informational only and the system does not read them, but external services such as Google Play do read them in order to provide filtering for users when they search for applications from their device.For example, if your application requires a camera and uses APIs introduced in Android7, you should declare these as requirements in your manifest file. That way, devices that do not have a camera and have an Android version lower than cannot install your application from Google Play.However, you can also declare that your application uses the camera, but doesnot require it. In that case, your application must perform a check at runtime to determineif the device has a camera and disable any features that use the camera if one is not available.Here are some of the important device characteristics that you should consider as you design and develop your application:Screen size and densityIn order to categorize devices by their screen type, Android defines two characteristics for each device: screen size the physical dimensions of the screen and screen density the physical density of the pixels on the screen, or dpi—dots per inch. To simplify all the different types of screen configurations, the Android system generalizes them into select groups that make them easier to target.The screen sizes are: small, normal, large, and extra large.The screen densities are: low density, medium density, high density, and extra high density.By default, your application is compatible with all screen sizes and densities, because the Android system makes the appropriate adjustments to your UI layout and image resources. However, you should create specialized layouts for certain screen sizes and provide specialized images for certain densities, using alternative layout resources, and by declaring in your manifest exactly which screen sizes your application supports with the element.For more information, see the document.Input configurationsMany devices provide a different type of user input mechanism, such as a hardware keyboard, a trackball, or a five-way navigation pad. If your application requires a particular kind of input hardware, then you should declare it in your manifest with the element. However, it is rare that an application should require a certain input configuration.Device featuresThere are many hardware and software features that may or may not existon a given Android-powered device, such as a camera, a light sensor, bluetooth, a certain version of OpenGL, or the fidelity of the touchscreen. You should never assume that a certain feature is available on all Android-powered devices other than the availability of the standard Android library, so you should declare any features used by your application with theelement.Platform VersionDifferent Android-powered devices often run different versions of the Android platform, such as Android or Android . Each successive version often includes additional APIs not available in the previous version. In order to indicate which set of APIs are available, each platform version specifies anfor example, Android is API Level 1 and Android is API Level 9. If you use any APIs that were added to the platform after version , you should declare the minimum API Level in which those APIs were introduced using theelement.It's important that you declare all such requirements for your application, because, when you distribute your application on Google Play, the store uses these declarations to filter which applications are available on each device. As such, your application should be available only to devices that meet all your application requirements.For more information about how Google Play filters applications based on these and other requirements, see the document.Application ResourcesAn Android application is composed of more than just code—it requires resources that are separate from the source code, such as images, audio files, and anything relating to the visual presentation of the application. For example, you should define animations, menus, styles, colors, and the layout of activity user interfaces with XML files. Using application resources makes it easy to update various characteristics of your applicationwithout modifying code and—by providing sets of alternative resources—enables you to optimize your application for a variety of device configurations such as different languages and screen sizes.For every resource that you include in your Android project, the SDK build tools define a unique integer ID, which you can use to reference the resource from your application code or from other resources defined in XML. For example, if your application c ontains an image file named saved in the res/drawable/ directory, the SDK tools generate a resource IDOne of the most important aspects of providing resources separate from your source code is the ability for you to provide alternative resources for different device configurations. For example, by defining UI strings in XML, you can translate the strings into other languages and save those strings in separate files. Then, based on a language qualifier that you append to the resource directory's name such as res/values-fr/ for French string values and the user's language setting, the Android system applies the appropriate language strings to your UI.Android supports many different qualifiers for your alternative resources. The qualifier is a short string that you include in the name of your resource directories in order to define the device configuration for which those resources should be used. As another example, you should often create different layouts for your activities, depending on the device's screen orientation and size. For example, when the device screen is in portrait orientation tall, you might want a layout with buttons to be vertical, but when the screen is in landscape orientation wide, the buttons should be aligned horizontally. To change the layout depending on the orientation, you can define two different layouts and apply the appropriate qualifier to each layout's directory name. Then, the system automatically applies the appropriate layout depending on the current device orientation.For more about the different kinds of resources you can include in your application and how to create alternative resources for various device configurations, see thedeveloper guide.安卓应用基础在Java编程语言编写的Android应用程序的Android的SDK工具编译代码以及与任何数据和到一个Android的包,一个归档文件档案资源的.apk后缀,所有的在一个单一的代码.apk文件被认为是一个应用程序,是Android的文件,供电设备来安装应用程序;一旦安装在设备上,每个Android应用程序的生命在它自己的安全沙箱：而Android操作系统是一个多用户Linux系统中,每个应用程序是一个不同的用户;默认情况下,每个应用程序的系统分配一个唯一的Linux用户ID该ID仅用于由系统是未知的应用程序,系统设置所有的应用程序中的文件权限,以便只有用户ID分配给该应用程序可以访问它们;每个进程都有它自己的虚拟机VM,因此应用程序的代码在从其他应用程序隔离运行;默认情况下,每个应用程序运行在它自己的Linux进程;Android的启动过程时,应用程序的任何组件需要被执行,然后关闭该进程时,它不再需要或恢复时,系统必须为其他应用程序的内存;这样一来,Android系统实现了最小特权原则,也就是说,每个应用程序,默认情况下,只能访问的组件,它需要做的工作,没有更多,这将创建一个非常安全的环境,使应用程序无法访问的,这就是它没有给予许可制度的部分;但是,有一个应用程序的方法与其他应用程序和应用程序访问系统服务的数据：这有可能为两个应用程序安排共享相同的Linux用户ID,在这种情况下,它们能够相互访问的文件;为了节约使用相同的用户ID系统资源,应用程序还可以安排运行在相同的Linux进程和共享同一个VM应用也必须使用相同的证书签名;应用程序可以请求访问权限,如用户的联系人,短信,可安装存储SD卡,摄像头,蓝牙等设备的数据,所有应用程序的权限必须由用户在安装时授予;这涵盖了基本就如何Android应用程序在系统中存在这个文件的其余部分向您介绍：1、框架的核心组件定义应用程序;2、清单文件中声明组件和应用程序所需的设备功能;3、资源是从应用程序代码分开,并允许您的应用程序正常优化的设备配置各种其行为;应用程序组件Application ComponentsAndroid的核心功能之一就是一个应用程序可以使用其它应用程序的元素如果那个应用程序允许的话;比如说,如果你的应用程序需要一个图片卷动列表,而另一个应用程序已经开发了一个合用的而又允许别人使用的话,你可以直接调用那个卷动列表来完成工作,而不用自己再开发一个;你的应用程序并没有吸纳或链接其它应用程序的代码,它只是在有需求的时候启动了其它应用程序的那个功能部分;为达到这个目的,系统必须在一个应用程序的一部分被需要时启动这个应用程序,并将那个部分的Java对象实例化;与在其它系统上的应用程序不同,Android应用程序没有为应用准备一个单独的程序入口比如说,没有main方法,而是为系统依照需求实例化提供了基本的组件;共有四种组件类型：活动Activities一个activity代表用户界面的一个独立屏幕;例如,一个邮件应用程序应该有一个activity 用于显示新邮件列表,另一个activity 用于撰写一封邮件,还有一个activity 用于读取邮件;尽管所有activitie 协同工作以构成邮件应用程序的用户体验,但彼此之间相对独立;应次,不同的应用程序能够从任何一个activity 启动只要邮件应用程序允许;例如,用户需要分享一张照片,一个拍照应用程序能够启动邮件应用程序的activity ;activity 是一个实现了的子类,你可以在开发者指导部分了解更多;服务Servicesservice是在后台运行,执行长时间操作或者执行远程操作; service 不提供用户界面;例如,当用户在另一个应用程序时,一个service 可在后台播放音乐,或者是从网络上获取数据,而不阻断用户与当前activity 的交互;其他组件,比如一个activity ,为了与该service 互动,可以启动或者绑定它;service是一个实现了的子类,你可以在开发者指导部分了解更多;广播接收器Broadcast receivers广播接收器是一个专注于接收广播通知信息,并做出对应处理的组件;很多广播是源自于系统代码的──比如,通知时区改变、电池电量低、拍摄了一张照片或者用户改变了语言选项;应用程序也可以进行广播──比如说,通知其它应用程序一些数据下载完成并处于可用状态;应用程序可以拥有任意数量的广播接收器以对所有它感兴趣的通知信息予以响应;所有的接收器均继承自基类;广播接收器没有用户界面;然而,它们可以启动一个activity来响应它们收到的信息,或者用来通知用户;通知可以用很多种方式来吸引用户的注意力──闪动背灯、震动、播放声音等等;一般来说是在状态栏上放一个持久的图标,用户可以打开它并获取消息;内容提供者Content providers内容提供者将一些特定的应用程序数据供给其它应用程序使用;数据可以存储于文件系统、SQLite数据库或其它方式;内容提供者继承于基类,为其它应用程序取用和存储它管理的数据实现了一套标准方法;然而,应用程序并不直接调用这些方法,而是使用一个对象,调用它的方法作为替代;ContentResolver可以与任意内容提供者进行会话,与其合作来对所有相关交互通讯进行管理;参阅独立的章节获得更多关于使用内容提供者的内容;每当出现一个需要被特定组件处理的请求时,Android会确保那个组件的应用程序进程处于运行状态,或在必要的时候启动它;并确保那个相应组件的实例的存在,必要时会创建那个实例;Android系统设计的一个独特方面是任何的一个程序都可以启动另一程序的组件;比如,你想让你的程序可以使用照相机拍照,如果已经有了实现这种功能的程序并且你你的程序能使用它有权限,那么你就没有再要再写一个新的Activity来实现这个功能;你的程序不需要包含或者链接这个拍照程序;相反,你只需要在你的程序中打开这个拍照程序中的实现拍照功能的Activity;当拍完之后,拍好的照片甚至会自动返回给你的程序;者对于用户来说,就好像是想拍照功能的程序就是你的这个程序的一部分一样;当系统启动一个组件之后,如果这个组件所在的程序之前没有运行的话,系统会自动开始这个程序的进程,并初始化这个组件所需要的相关类;比如,你的程序开启了一个拍照功能程序的Activity,这时系统会启动这个Activity所在的程序,所以这个Activity运行在拍照功能的程序当中,而不是在你的程序中;所以,不像其他操作系统的中的程序一样,Android程序没有一个单独的入口点比如没有我们常见的main函数;因为系统中的程序运行在自己的独立进程中,并且程序中的文件都有自己的限制其他程序访问的权限,所以,你的程序不能直接激活其他程序中的组件;但是Android系统就可以;具体是这样的实现的,为了激活activate其他程序中的组件,你必须向系统发送一个消息来详细说明你要启动其他组件的意图,这样系统才会为你激活这个组件;激活组件Activating Components四大组件中的三个组件——activities、services和broadcast receiver——是由一种叫intent的异步消息来激活的;这些intents在运行时runtime将这些属于你的程序或不同程序的单独的组件绑定在一起bind,你可以把这些intents看作是需要其他组件的action的messengers;一个intent就是一个Intent对象,这个intent定义了一种可以激活activate某个特定组件或者某种特定类型的组件,这两种情况分别对应两种intent的定义方式或者显示的或者隐式的;对于activities和services,一个intent定义了要执行的操作action比如,要“view”或者“send”什么和要操作的数据的URI;比如,一个intent可能会为一个activity传递一个请求来展示一张图片或者打开一个网页;有时,你可以启动一个activity来得到返回的结果,在这个例子中这个activity的返回的结果也是一个Intent比如,你可以发送一个intent让用户选择一个personal contact并返回给你——这个返回的intent就包含了一个指向用户选择的联系人的URI;关于activity和service的启动方式,下面将介绍;对于广播接收者来说,intent只是简单的定义了要广播的内容比如,一个用以表明电池电量很低的广播仅包含了一个表明电池电量很低的字符串;最后一种组件类型content provider并不是由intent来激活的activate;而是由接收到ContentResolver的请求时激活的;它们都各自有自己的方法来激活相应的组件：你可以通过传递一个Intent给startActivity或startActivityForResult启动一个activity或者给他一些新的要做的内容;使用startActivityForResult你将得到一个返回结果;你可以通过传递一个Intent给startService来start一个service或者给一个正在运行的service一些新的指令instructions;或者你可以通过把一个Intent传递给bindService来绑定一个service;你可以通过传递一个Intent给诸如sendBroadcast、sendOrderedBroadcast或者sendStickyBroadcast等方法来初始化一个广播;你可以通过调用ContentResolver的query方法来执行一次content provider的查询操作;更多的关于intent的内容,可以参看文档中的IntentsandIntentFilters;更多的关于激活特定组件的内容可以参看文档中的：Activities、Services、BroadcastReceiver、ContentProviders;关于Manifest文件在Android系统可以启动一个应用程序组件之前,Android系统必须通过读取这个程序的即manifest文件文件来确定要启动的组件存在;你的程序必须在这个manifest文件声明用到的所有的组件,并且这个manifest文件必须在项目的根目录下;另外,这个manifest文件还声明一些其他的东西,比如：确定这个程序需要的所有权限,比如Internet访问权限或者读取用户联系人权限;声明这个运行这个程序所需要的最低API版本,这个可以根据开发该程序所使用的API版本;声明该程序所需要的硬件或软件特征features,比如照相机、蓝牙服务或者多点触屏;声明该程序需要链接linkagainst的API库不是Andorid的frameworkAPIs,比如GoogleMapslibrary;组件声明Manifest文件的首要任务就是通知系统关于程序中要使用的组件;比如,一个manifest文件可以用如下的方式来声明一个activity：java1.<xml version=""2.encoding="utf-8">3.<manifest...>4.<application android:icon="drawable/"...>5.android:label="string/example_label"...>6.</activity>7....8.</application>9.</manifest>在<application>元素中,android:icon属性用于指定一个用于标示该程序的icon;在<activity>元素中,android:name属性用于确定这个扩展自Activity的子类的全路径名,android:label属性用于标示这个activity的对于用户可见的label;你必须要用以下方式来声明你的程序组件：1、activities：<activity>标签2、services:<service>标签3、broadcast receiver：<receiver>标签4、content providers：<provider>标签如果程序中用到activities、services和content providers,你没有在manifest文件中声明,那么这些组件将不会被系统知道,结果就是你的程序不能运行;然而,broadcast receiver既可以在manifest文件中声明也可以在代码中动态创建BroadcastReceiver,并通过调用registerReceiver在系统中注册;更多关于怎样为你的程序构建manifest文件,请参看文档The 文件;声明组件的能力正如在上面ActivatingComponents中讨论的那样,你可以使用一个Intent来启动activities、services和broadcastreceiver;你可以通过在intent中注明目标组件的名字使用的是组件的类名来显示的启动组件;然而,intents真正强大的地方在与关于intent 的actions的概念;通过intent的actions,你可以简单的描述你要执行的操作的类型并且可以有选择的描述你要处理的数据,可以允许系统在device中找到这个组件并启动它;如果有多个组件可以执行intent中描述的action,这时用户就可以选择一个来执行;系统可以识别能对某intent做出反应的方式是通过将接收到的intent和设备中其他程序的manifest文件的intent filters进行比较实现的;当你在程序的manifest文件中声明一个组件之后,你可以有选择包含intentfilters,这些intentfilters表明了组件对接收自其他程序的intent做出反应的能力capabilities;你可以通过添加一个<intent-filter>元素作为achildofthecomponent'sdeclarationelement 来为你的程序声明一个intentfilter;比如,在一个邮件程序中的一个activity可以编写新的邮件,这样的话你就需要在manifest文件中来声明一个intent filter来对“发送”intent响应为了发送邮件;这样,在你的程序中,一个activity就可以创建一个发送intentACTION_SEND,这样当你调用startaActivity时,系统就会匹配邮件程序中的发送activity并启动它;更多关于创建intentfilters的内容,可以参看IntentsandIntentFilter文档;声明运行程序所需的条件Andorid系统可以支持很多不同的设备,并且这些设备的性能特征并不相同;为了防止你的程序被安装在不能正常运行你的程序的较低android系统版本上,通过在manifest文件中声明你的程序支持的设备和软件,便变得尤其重要起来;大多数的这些声明仅是一些信息,而系统并不会读取它们,但是其他的服务比如Android Market 却会阅读这些声明来帮助通过通过自己的设备搜索软件的用户过滤软件;比如,你的程序需要照相机,并且使用的的APIs,那么你就必须在你的manifest文件中声明这些需要;这样的话,在Android Market上,没有照相机或者Android系统版本低于将不能安装你的程序;然而,如果你的程序不需要照相机,你仍可以声明你需要照相机;这种情况下,你的程序必须在运行时做一下检查,来检查这个设备是否含有照相机,如果没有照相机可用,则系统将会使使用照相机的相关程序不能用;下面是一些你在设计和开发你的程序时,必须要考虑的关于设备的一些重要方面：屏幕大小和分辨率：为了根据屏幕的类型进行分类,Android定义了两个特征：屏幕大小和分辨率;屏幕尺寸有：小,中,大,超大；屏幕分辨率类型：低分辨率,中分辨率,高分辨率,超高分辨率；默认情况下,你的程序可以兼容所有的屏幕尺寸和分辨率,因为Android系统对你的程序的UI布局和image资源做了适当的调整;输入方式：。

随着社会经济的发展以及科学技术的进步，智能手机以及个人电脑被广泛应用在人们的日常生产生活中。

安卓操作系统作为智能的操作系统，其具有高度的开放性，使得智能手机以及个人电脑具有较大的应用优势，下面是安卓开发英文参考文献，欢迎借鉴参考。

安卓开发英文参考文献一： [1]Haomin Song,Duanqing Xu. The Design and Development of a Full Range of Display System for 3D Images Based on AndroidSmartphone[P]. Proceedings of the International Conference on Education, Management, Commerce and Society,2015. [2]Iva Evry Robyansah. The Development of “Ayo Membaca” Android Application for Reading Assessment[P]. Proceedings of the 2nd International Conference on Education Innovation (ICEI 2018),2018. [3]Qingru Lu,Haiyan Xin,Hui Huang,Yunlong Geng. Design and Development of Multifunction Map Software Based on AndroidPlatform[P]. Proceedings of the 2015 International Conference on Electromechanical Control Technology and Transportation,2015. [4]Hongsheng Zhang. Research on Software Development and Test Environment Automation based on Android Platform[P]. Proceedings of the 3rd International Conference on Mechatronics Engineering and Information Technology (ICMEIT 2019),2019. [5]Yong-fei Ye,Ming-he Liu,Xiao Zhang,Xing-hua Sun,Nai-di Liu. Application and Research of Blended Teaching Model in Programming Courses --- Android Application Development Course as an Example[P]. Proceedings of the 3d International Conference on Applied Social Science Research,2016. [6]Xinge Li. The development of designated driving application based on Android platform and Ali cloud sever[P]. Proceedings of the 2016 2nd Workshop on Advanced Research and Technology in Industry Applications,2016. [7]Winda Dwi Fitria,Achmad Lutfi. Development Of Wind’s Maze Chemistry Game Based On Android As A Learning Media On Hydrocarbon Matter For Eleventh Grade Senior High School[P]. Proceedings of the Seminar Nasional Kimia - National Seminar on Chemistry (SNK2018),2018. [8]Fuling Li,Yong Li. Development of Mobile Security Guard Based on Android System[P]. Proceedings of the 2015 International Conference on Automation, Mechanical Control and Computational Engineering,2015. [9]Qinhua Lin. 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英语原文Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package, an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application.Once installed on a device, each Android application lives in its own security sandbox:●The Android operating system is a multi-user Linux system in which eachapplication is a different user.●By default, the system assigns each application a unique Linux user ID (the ID isused only by the system and is unknown to the application). The system setspermissions for all the files in an application so that only the user ID assigned to thatapplication can access them.●Each process has its own virtual machine (VM), so an application's code runs inisolation from other applications.●By default, every application runs in its own Linux process. Android starts theprocess when any of the application's components need to be executed, then shutsdown the process when it's no longer needed or when the system must recovermemory for other applications.In this way, the Android system implements the principle of least privilege. That is, each application, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an application cannot access parts of the system for which it is not given permission.However, there are ways for an application to share data with other applications and for an application to access system services:●It's possible to arrange for two applications to share the same Linux user ID, in whichcase they are able to access each other's files. To conserve system resources,applications with the same user ID can also arrange to run in the same Linux processand share the same VM (the applications must also be signed with the samecertificate).●An application can request permission to access device data such as the user'scontacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, andmore. All application permissions must be granted by the user at install time.That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to:●The core framework components that define your application.●The manifest file in which you declare components and required device features foryour application.●Resources that are separate from the application code and allow your application togracefully optimize its behavior for a variety of device configurations.Application ComponentsApplication components are the essential building blocks of an Android application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each one exists as its own entity and plays a specific role—each one is a unique building block that helps define your application's overall behavior.There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.Here are the four types of application components:ActivitiesAn activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. As such, a different application can start any one of these activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture.An activity is implemented as a subclass of Activity and you can learn more about it in the Activities developer guide.ServicesA service is a component that runs in the background to perform long-runningoperations or to perform work for remote processes. A service does not provide a user interface. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. Another component, such as an activity, can start the service and let it run or bind to it in order to interact with it.A service is implemented as a subclass of Service and you can learn more about it inthe Services developer guide.Content providersA content provider manages a shared set of application data. You can store the data inthe file system, an SQLite database, on the web, or any other persistent storage location your application can access. Through the content provider, other applications can query or even modify the data (if the content provider allows it). For example, the Android system provides a content provider that manages the user's contact information. As such, any application with the proper permissions can query part of the content provider (such as ContactsContract.Data) to read and write information about a particular person.Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the Note Pad sample application uses a content provider to save notes.A content provider is implemented as a subclass of ContentProvider and mustimplement a standard set of APIs that enable other applications to perform transactions.For more information, see the Content Providers developer guide.Broadcast receiversA broadcast receiver is a component that responds to system-wide broadcastannouncements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture wascaptured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs.More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service to perform some work based on the event.A broadcast receiver is implemented as a subclass of BroadcastReceiver and eachbroadcast is delivered as an Intent object. For more information, see the BroadcastReceiver class.A unique aspect of the Android system design is that any application can start another application’s component. For example, if you want the user to capture a photo with the device camera, there's probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You don't need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application.When the system starts a component, it starts the process for that application (if it's not already running) and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your application's process. Therefore, unlike applications on most other systems, Android applications don't have a single entry point (there's no main()function, for example).Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies your intent to start a particular component. The system then activates the component for you.Activating ComponentsThree of the four component types—activities, services, and broadcast receivers—are activated by an asynchronous message called an intent. Intents bind individual components to each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another.An intent is created with an Intent object, which defines a message to activate either a specific component or a specific type of component—an intent can be either explicit or implicit, respectively.For activities and services, an intent defines the action to perform (for example, to "view" or "send" something) and may specify the URI of the data to act on (among other things that the component being started might need to know). For example, an intent might convey a request for an activity to show an image or to open a web page. In some cases, you can start an activity to receive a result, in which case, the activity also returns the result inan Intent (for example, you can issue an intent to let the user pick a personal contact and have it returned to you—the return intent includes a URI pointing to the chosen contact).For broadcast receivers, the intent simply defines the announcement being broadcast (for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low").The other component type, content provider, is not activated by intents. Rather, it is activated when targeted by a request from a ContentResolver. T he content resolver handles all direct transactions with the content provider so that the component that's performing transactions with the provider doesn't need to and instead calls methods onthe ContentResolver object. This leaves a layer of abstraction between the content provider and the component requesting information (for security).There are separate methods for activating each type of component:•You can start an activity (or give it something new to do) by passingan Intent to startActivity() or startActivityForResult() (when you want the activity toreturn a result).•You can start a service (or give new instructions to an ongoing service) by passing an Intent to startService(). Or you can bind to the service by passingan Intent to bindService().•You can initiate a broadcast by passing an Intent to methodslike sendBroadcast(), sendOrderedBroadcast(), or sendStickyBroadcast().•You can perform a query to a content provider by calling query() ona ContentResolver.For more information about using intents, see the Intents and Intent Filters document. More information about activating specific components is also provided in the following documents: Activities, Services, BroadcastReceiver and Content Providers.Declaring componentsThe primary task of the manifest is to inform the system about the application's components. For example, a manifest file can declare an activity as follows:In the <application> element, the android:icon attribute points to resources for an icon that identifies the application.In the <activity> element, the android:name at tribute specifies the fu lly qualified class name of the Activity subclass and the android:label attributes specifies a string to use as the user-visible label for the activity.You must declare all application components this way:●<activity>elements for activities●<service> elements for services●<receiver>elements for broadcast receivers<provider>elements for content providersActivities, services, and content providers that you include in your source but do not declare in the manifest are not visible to the system and, consequently, can never run. However, broadcast receivers can be either declared in the manifest or created dynamically in code (as BroadcastReceiver objects) and registered with the system bycalling registerReceiver().Declaring component capabilitiesAs discussed above, in Activating Components, you can use an Intent to start activities, services, and broadcast receivers. You can do so by explicitly naming the target component (using the component class name) in the intent. However, the real power of intents lies in the concept of intent actions. With intent actions, you simply describe the type of action you want to perform (an d optionally, the data upon which you’d like to perform the action) and allow the system to find a component on the device that can perform the action and start it. If there are multiple components that can perform the action described by the intent, then the user selects which one to use.The way the system identifies the components that can respond to an intent is by comparing the intent received to the intent filters provided in the manifest file of other applications on the device.When you declare a component in your application's manifest, you can optionally include intent filters that declare the capabilities of the component so it can respond to intents from other applications. You can declare an intent filter for your component by addingan <intent-filter>element as a child of the component's declaration element.For example, an email application with an activity for composing a new email might declare an intent filter in its manifest entry to respond to "send" intents (in order to send email). A n activity in your application can then create an intent with the “send” action (ACTION_SEND), which the system matches to the email application’s “send” a ctivity and launches it when you invoke the intent with startActivity().For more about creating intent filters, see the Intents and Intent Filters document.Declaring application requirementsThere are a variety of devices powered by Android and not all of them provide the same features and capabilities. In order to prevent your application from being installed on devices that lack features needed by your application, it's important that you clearly define a profile for the types of devices your application supports by declaring device and software requirements in your manifest file. Most of these declarations are informational only and the system does not read them, but external services such as Google Play do read them in order to provide filtering for users when they search for applications from their device.For example, if your application requires a camera and uses APIs introduced in Android 2.1 (API Level 7), you should declare these as requirements in your manifest file. That way, devices that do not have a camera and have an Android version lower than 2.1 cannot install your application from Google Play.However, you can also declare that your application uses the camera, but doesnot require it. In that case, your application must perform a check at runtime to determine if the device has a camera and disable any features that use the camera if one is not available.Here are some of the important device characteristics that you should consider as you design and develop your application:Screen size and densityIn order to categorize devices by their screen type, Android defines two characteristics for each device: screen size (the physical dimensions of the screen) and screen density (the physical density of the pixels on the screen, or dpi—dots per inch). To simplify all the different types of screen configurations, the Android system generalizes them into select groups that make them easier to target.The screen sizes are: small, normal, large, and extra large.The screen densities are: low density, medium density, high density, and extra highdensity.By default, your application is compatible with all screen sizes and densities, because the Android system makes the appropriate adjustments to your UI layout and imageresources. However, you should create specialized layouts for certain screen sizes and provide specialized images for certain densities, using alternative layout resources,and by declaring in your manifest exactly which screen sizes your application supports with the <supports-screens> element.For more information, see the Supporting Multiple Screens document.Input configurationsMany devices provide a different type of user input mechanism, such as a hardware keyboard, a trackball, or a five-way navigation pad. If your application requires a particular kind of input hardware, then you should declare it in your manifest with the <uses-configuration> e lement. However, it is rare that an application should require a certain input configuration.Device featuresThere are many hardware and software features that may or may not exist on a given Android-powered device, such as a camera, a light sensor, bluetooth, a certain version of OpenGL, or the fidelity of the touchscreen. You should never assume that a certain feature is available on all Android-powered devices (other than the availability of the standard Android library), so you should declare any features used by your application with the <uses-feature> element.Platform VersionDifferent Android-powered devices often run different versions of the Android platform, such as Android 1.6 or Android 2.3. Each successive version often includes additional APIs not available in the previous version. In order to indicate which set of APIs are available, each platform version specifies an API Level (for example, Android 1.0 is API Level 1 and Android 2.3 is API Level 9). If you use any APIs that were added to the platform after version 1.0, you should declare the minimum API Level in which those APIs were introduced using the <uses-sdk> element.It's important that you declare all such requirements for your application, because, when you distribute your application on Google Play, the store uses these declarations to filter which applications are available on each device. As such, your application should be available only to devices that meet all your application requirements.For more information about how Google Play filters applications based on these (and other) requirements, see the Filters on Google Play document.Application ResourcesAn Android application is composed of more than just code—it requires resources that are separate from the source code, such as images, audio files, and anything relating to the visual presentation of the application. For example, you should define animations, menus, styles, colors, and the layout of activity user interfaces with XML files. Using application resources makes it easy to update various characteristics of your application without modifying code and—by providing sets of alternative resources—enables you to optimize your application for a variety of device configurations (such as different languages and screen sizes).For every resource that you include in your Android project, the SDK build tools define a unique integer ID, which you can use to reference the resource from your application code or from other resources defined in XML. For example, if your application c ontains an image file named logo.png (saved in the res/drawable/ directory), the SDK tools generate a resource ID named , which you can use to reference the image and insert it in your user interface.One of the most important aspects of providing resources separate from your source code is the ability for you to provide alternative resources for different device configurations. For example, by defining UI strings in XML, you can translate the strings into other languages and save those strings in separate files. Then, based on a language qualifier that you append to the resource directory's name (such as res/values-fr/for French string values) and the user's language setting, the Android system applies the appropriate language strings to your UI.Android supports many different qualifiers for your alternative resources. The qualifier is a short string that you include in the name of your resource directories in order to define the device configuration for which those resources should be used. As another example, you should often create different layouts for your activities, depending on the device's screen orientation and size. For example, when the device screen is in portrait orientation (tall), you might want a layout with buttons to be vertical, but when the screen is in landscape orientation (wide), the buttons should be aligned horizontally. To change the layout depending on the orientation, you can define two different layouts and apply the appropriate qualifier to each layout's directory name. Then, the system automatically applies the appropriate layout depending on the current device orientation.For more about the different kinds of resources you can include in your application and how to create alternative resources for various device configurations, see the Application Resources developer guide.中文译文安卓应用基础Android应用程序是用Java编程语言编写的，Android的SDK工具编译成代码和数据和资源文件放到一个Android的包，一个归档文件档案资源的.apk后缀，所有的在一个单一的代码.apk文件被认为是一个应用程序，是Android的文件，供电设备来安装应用程序。

AndroidAndroid, as a system, is a Java-based operating system that runs on the Linux 2.6 kernel. The system is very lightweight and full featured. Android applications are developed using Java and can be ported rather easily to the new platform. If you have not yet downloaded Java or are unsure about which version you need, I detail the installation of the development environment in Chapter 2. Other features of Android include an accelerated 3-D graphics engine (based on hardware support), database support powered by SQLite, and an integrated web browser.If you are familiar with Java programming or are an OOP developer of any sort, you are likely used to programmatic user interface (UI) development—that is, UI placement which is handled directly within the program code. Android, while recognizing and allowing for programmatic UI development, also supports the newer, XML-based UI layout. XML UI layout is a fairly new concept to the average desktop developer. I will cover both the XML UI layout and the programmatic UI development in the supporting chapters of this book.One of the more exciting and compelling features of Android is that, because of its architecture, third-party applications—including those that are “home grown”—are executed with the same system priority as those that are bundled with the core system. This is a major departure from most systems, which give embedded system apps a greater execution priority than the thread priority available to apps created by third- party developers. Also, each application is executed within its own thread using a very lightweight virtual machine.Aside from the very generous SDK and the well-formed libraries that are available to us to develop with, the most exciting feature for Android developers is that we now have access to anything the operating system has access to. In other words, if you want to create an application that dials the phone, you have access to the phone’s dialer; if you want to create an application that utilizes the phone’s internalGPS (if equipped), you have access to it. The potential for developers to create dynamic and intriguing applications is now wide open.On top of all the features that are available from the Android side of the equation, Google has thrown in some very tantalizing features of its own. Developers of Android applications will be able to tie their applications into existing Google offerings such as Google Maps and the omnipresent Google Search. Suppose you want to write an application that pulls up a Google map of where an incoming call is emanating from, or you want to be able to store common search results with your contacts; the doors of possibility have been flung wide open with Android.Chapter 2 begins your journey to Android development. You will learn the how’s and why’s of using specific development environments or integrated development environments (IDE), and you will download and install the Java IDE Eclipse.Application ComponentsA central feature of Android is that one application can make use of elements of other applications (provided those applications permit it). For example, if your application needs to display a scrolling list of images and another application has developed a suitable scroller and made it available to others, you can call upon that scroller to do the work, rather than develop your own. Your application doesn't incorporate the code of the other application or link to it. Rather, it simply starts up that piece of the other application when the need arises.For this to work, the system must be able to start an application process when any part of it is needed, and instantiate the Java objects for that part. Therefore, unlike applications on most other systems, Android applications don't have a single entry point for everything in the application (no main() function, for example). Rather, they have essential components that the system can instantiate and run as needed. There are four types of components:ActivitiesAn activity presents a visual user interface for one focused endeavor the user can undertake. For example, an activity might present a list of menu items users can choose from or it might display photographs along with their captions. A text messaging application might have one activity that shows a list of contacts to send messages to, a second activity to write the message to the chosen contact, and other activities to review old messages or change settings. Though they work together to form a cohesive user interface, each activity is independent of the others. Each one is implemented as a subclass of the Activity base class.An application might consist of just one activity or, like the text messaging application just mentioned, it may contain several. What the activities are, and how many there are depends, of course, on the application and its design. Typically, one of the activities is marked as the first one that should be presented to the user when the application is launched. Moving from one activity to another is accomplished by having the current activity start the next one.Each activity is given a default window to draw in. Typically, the window fills the screen, but it might be smaller than the screen and float on top of other windows. An activity can also make use of additional windows — for example, a pop-up dialog that calls for a user response in the midst of the activity, or a window that presents users with vital information when they select a particular item on-screen.The visual content of the window is provided by a hierarchy of views — objects derived from the base View class. Each view controls a particular rectangular space within the window. Parent views contain and organize the layout of their children. Leaf views (those at the bottom of the hierarchy) draw in the rectangles they control and respond to user actions directed at that space. Thus, views are where the activity's interaction with the user takes place.For example, a view might display a small image and initiate an action when theuser taps that image. Android has a number of ready-made views that you can use —including buttons, text fields, scroll bars, menu items, check boxes, and more.A view hierarchy is placed within an activity's window by the Activity.setContentView() method. The content view is the View object at the root of the hierarchy. (See the separate User Interface document for more information on views and the hierarchy.)ServicesA service doesn't have a visual user interface, but rather runs in the background for an indefinite period of time. For example, a service might play background music as the user attends to other matters, or it might fetch data over the network or calculate something and provide the result to activities that need it. Each service extends the Service base class.A prime example is a media player playing songs from a play list. The player application would probably have one or more activities that allow the user to choose songs and start playing them. However, the music playback itself would not be handled by an activity because users will expect the music to keep playing even after they leave the player and begin something different. To keep the music going, the media player activity could start a service to run in the background. The system would then keep the music playback service running even after the activity that started it leaves the screen.It's possible to connect to (bind to) an ongoing service (and start the service if it's not already running). While connected, you can communicate with the service through an interface that the service exposes. For the music service, this interface might allow users to pause, rewind, stop, and restart the playback.Like activities and the other components, services run in the main thread of the application process. So that they won't block other components or the user interface, they often spawn another thread for time-consuming tasks (like music playback). SeeProcesses and Threads, later.Broadcast receiversA broadcast receiver is a component that does nothing but receive and react to broadcast announcements. Many broadcasts originate in system code — for example, announcements that the timezone has changed, that the battery is low, that a picture has been taken, or that the user changed a language preference. Applications can also initiate broadcasts — for example, to let other applications know that some data has been downloaded to the device and is available for them to use.An application can have any number of broadcast receivers to respond to any announcements it considers important. All receivers extend the BroadcastReceiver base class.Broadcast receivers do not display a user interface. However, they may start an activity in response to the information they receive, or they may use the NotificationManager to alert the user. Notifications can get the user's attention in various ways — flashing the backlight, vibrating the device, playing a sound, and so on. They typically place a persistent icon in the status bar, which users can open to get the message.Content providersA content provider makes a specific set of the application's data available to other applications. The data can be stored in the file system, in an SQLite database, or in any other manner that makes sense. The content provider extends the ContentProvider base class to implement a standard set of methods that enable other applications to retrieve and store data of the type it controls. However, applications do not call these methods directly. Rather they use a ContentResolver object and call its methods instead. A ContentResolver can talk to any content provider; it cooperates with the provider to manage any interprocess communication that's involved.See the separate Content Providers document for more information on usingcontent providers.Whenever there's a request that should be handled by a particular component, Android makes sure that the application process of the component is running, starting it if necessary, and that an appropriate instance of the component is available, creating the instance if necessary.Key Skills & Concepts●Creating new Android projects●Working with Views●Using a TextView●Modifying the main.xml fileCreating Your First Android Project in EclipseTo start your first Android project, open Eclipse. When you open Eclipse for the first time, it opens to an empty development environment (see Figure 5-1), which is where you want to begin. Your first task is to set up and name the workspace for your application. Choose File | New | Android Project, which will launch the New Android Project wizard.CAUTION Do not select Java Project from the New menu. While Android applications are written in Java, and you are doing all of your development in Java projects, this option will create a standard Java application. Selecting Android Project enables you to create Android-specific applications.If you do not see the option for Android Project, this indicates that the Android plugin for Eclipse was not fully or correctly installed. Review the procedure in Chapter 3 for installing the Android plugin for Eclipse to correct this.The New Android Project wizard creates two things for youA shell application that ties into the Android SDK, using the android.jar file, andties the project into the Android Emulator. This allows you to code using all of the Android libraries and packages, and also lets you debug your applications in the proper environment.Your first shell files for the new project. These shell files contain some of the vital application blocks upon which you will be building your programs. In much the same way as creating a Microsoft .NET application in Visual Studio generates some Windows-created program code in your files, using the Android Project wizard in Eclipse generates your initial program files and some Android-created code. In addition, the New Android Project wizard contains a few options, shown next, that you must set to initiate your Android project. For the Project Name field, for purposes of this example, use the title HelloWorldText. This name sufficiently distinguishes this Hello World! project from the others that you will be creating in this chapter.In the Contents area, keep the default selections: the Create New Project in Workspace radio button should be selected and the Use Default Location check box should be checked. This will allow Eclipse to create your project in your default workspace directory. The advantage of keeping the default options is that your projects are kept in a central location, which makes ordering, managing, and finding these projects quite easy. For example, if you are working in a Unix-based environment, this path points to your $HOME directory.If you are working in a Microsoft Windows environment, the workspace path will be C:/Users/<username>/workspace, as shown in the previous illustration. However, for any number of reasons, you may want to uncheck the Use Default Location check box and select a different location for your project. One reason you may want to specify a different location here is simply if you want to choose a location for this specific project that is separate from other Android projects. For example, you may want to keep the projects that you create in this book in a different location from projects that you create in the future on your own. If so, simply override the Location option to specify your own custom location directory for this project.。

中英文对照外文翻译(文档含英文原文和中文翻译)1 什么是Android1.1 主要技巧和思想●历史的嵌入式器件编程●开放手机联盟的解释●第一眼看到Android的主屏幕可以这么说，暂时，传统的桌面应用程序开发者已经被惯坏了。

这个不是说桌面应用程序开发比其他形式的开发很简单。

总之，作为传统桌面的应用程序开发者，凡是我们能想象到的各种应用程序,我们就一定有能力创造。

包括我自己，因为我也是从做桌面程序开始的。

一方面已经使得桌面程序更容易理解就是我们已经有能力去跟桌面操作系统相互作用，因此，任何底部的硬件很自由的相互作用。

这种类型独立自主的程序编制，然而，对于很小的开发者团体来说是不敢冒险的去搞手机发展这样浑浊的技术的。

注解：我提到两种不同的开发商在此讨论:传统的桌面应用程序开发，他们能在任何语言环境下工作，而且最终的产品和程序是用来运行“桌面”操作系统的；还有Android 程序开发者，那些开发Android平台开发工具的JAVA程序开发人员。

这不是说跟其他人比起来谁好谁坏。

其实，区别目的仅仅在于想说明并比较Android桌面操作系统环境的开发风格，工具。

1.2 嵌入式器件编程的简要历史有很长一段时间，手机的开发者由大的著名嵌入式的开发团队中的少数人组成，作为嵌入式设备的开发者。

相对于桌面开发或者后续的网络开发，被视作更少“魅力”，而且嵌入式设备的开发通常因为硬件和操作系统而处于劣势。

因为嵌入式设备的制造商们太小气，他们要保护他们硬件方面的秘密，所以他们给开发者们非常有限的库去运行当他们尝试去让一些特定的设备去相互作用。

嵌入设备与桌面系统显著不同的一部分是嵌入设备是个有特色的“芯片上的电脑”。

例如：考虑你的标准电话遥控。

这个并不是一个非常强大并且复杂性的技术。

当任何的按钮被按下去，一个芯片解释一个信号以一种方式已经被编程进了这个设备。

这个允许设备知道什么是从输入设备（键盘）来的需要。

并且如何的响应这些命令（比如，打开电视机）。

中英文对照外文翻译文献(文档含英文原文和中文翻译)译文：深入理解安卓系统的安全性下一代开放操作系统的主流将不会在桌面上，但是将会出现在我们每天携带的手机上。

这些开放性的环境将会带领这些新的应用可能集成这些已经存在的在线服务，当然随着日以具增的数据与服务在手机上的支持，手机上的安全缺陷也越发明显。

下一代操作系统本质在于是否提供一个完整综合的安全平台。

由开放手机联盟（open Handset Alliance 谷歌领导）所开发的android 系统是一个被广泛看好的一个手机开源系统，该系统提供一个基本的操作系统，一个中间件应用层，一个java开发工具和一个系统应用收集器（collection of systemapplications ）。

尽管android SDK自2007年就发布了，但是第一部android 手机却在2008年10月才诞生。

自从这时起谷歌开起了自己的时代，T-Mobile的G1的制造商台湾HTC估算G1的发货量在2008年底已经超过100万部。

据业内人士预期该G1手机的销量将会在2009年继续保持。

不久的将来其他许多手机供应商要计划支持这个系统。

一个围绕android庞大的开发者社区已经建立，同时很多新的产品和应用已经可以在android上使用。

一个Android的主要卖点是它使开发人员无缝把在线服务扩展到手机。

这方面最明显的例子是谷歌的紧密集成Gmail，日历和联系人Web应用程序通过该系统。

用户只需提供一个android用户名和密码，其手机自动同步与谷歌的服务。

其他厂商正在迅速适应自己的现有的即时通讯，社交网络和游戏服务。

Android和许多企业寻找新途径来整合他们的自己已有的业务到android上。

传统的台式机和服务器的操作系统一直在努力进行安全功能的集成。

这些个人和商业应用在单一平台的很出色，然而这一块业务一个手机平台上像android上不是很有用。

它给了许多研究人员希望。

外文资料：WLANWhy use WLANFor one of the main local area network management, for the laying of cables, or check the cable is disconnected this time-consuming work, it is easy to upset, not easy to break in a short time to find out where. Furthermore, for the business and application environment constantly updating and development of enterprise network must be matched with the original re-layout, need to re-install the network lines, although the cable itself is not expensive, but requested the technical staff to the high cost of wiring, especially the old building, wiring project costs even higher. Therefore, the construction of wireless local area network has become the best solution.What conditions need to use WLANWLAN is not limited to alternative local area network, but to make up for lack of wired local area networks, in order to achieve the purpose of extending the network, the following circumstances may have wireless local area network.●no fixed workplace users●wired local area network set up by the environmental constraints●As a wired local area network backup systemWLAN access technologyCurrently manufacturers in the design of wireless local area network products, there are quite a variety of access design methods can be divided into three categories: narrowband microwave, spread spectrum (Spread Spectrum) technology, and infrared have their advantages and disadvantages, limitations, and more, followed by detailed discussion of these techniques. (Infrared) technology, each technique has their advantages and disadvantages, limitations, and more, followed by detailed discussion of these techniques.Technical requirementsAs wireless local area network needs to support high-speed, burst data services, need to be addressed in the indoor use of multipath fading, as well as issues such ascrosstalk subnets. Specifically, wireless local area network must achieve the following technical requirements:1)Reliability: Wireless LAN system packet loss rate should be lower than 10-5,the error rate should be lower than 10-8.2)Compatibility: For indoor use of wireless local area network, so as far aspossible with the existing wired LAN network operating system and networksoftware compatible.3)Data rate: In order to meet the needs of local area network traffic, wirelessLAN data transfer rate should be more than 1Mbps.4)The confidentiality of communications: As the data transmitted in the air viawireless media, wireless local area networks at different levels must takeeffective measures to improve communication security and data security.5)Mobility: support for all mobile networks or semi-mobile network.6)Energy Management: When receiving or sending data to the site when themachine is in sleep mode, when activated again when the data transceiver toachieve the savings in power consumption.7)small size and low price: This is the key to the popularity of wireless local areanetwork can be.8)Electromagnetic environment: wireless LAN should consider thehumanbodyand the surrounding electromagnetic environment effects.AndroidGoogle Android is a Linux-based platform for developing open-source phone operating system (registered trademark in China called &quot;Achi;). It includes operating systems, user interface and applications - mobile phone work required by the software, but there is no past, the exclusive right to impede innovation and barriers to mobile industry, called mobile terminal is the first to create a truly open and complete mobile software. Google and Open Handset Alliance to develop the Android, the alliance by including China Mobile, Motorola, Qualcomm and T-Mobile, including more than 30 technology and the composition of a leader in wireless applications. Google with operators, equipment manufacturers, developers and other interested parties to formdeep-level partnerships, hoping to establish a standardized, open software platform for mobile phones in the mobile industry to form an open ecosystem .It uses software stack layers (software stack, also known as the software stack) architecture, is divided into three parts: the core of the underlying Linux-based language developed by the c, only basic functions. Middle layer consists of library. Library and Virtual Machine Virtual Machine, developed by the C +. At the top are a variety of applications, including the call procedures, SMS procedures, application software is developed by the companies themselves to write java.To promote this technology, Google, and dozens of other phone company has established the Open Handset Alliance (Open Handset Alliance).Characteristic●application framework to support component reuse and replacement●Dalvik virtual machine specifically for mobile devices is optimized●Internal integrated browser, the browser-based open-source WebKit engine●optimization of 2D and 3D graphics library includes graphics library, 3Dgraphics library based on OpenGL ES 1.0 (hardware-accelerated optional)●# SQLite for structured data storage●Multimedia support includes the common audio, video and static image fileformats (such as MPEG4, H.264, MP3, AAC, AMR, JPG, PNG, GIF)●GSM phone (depending on hardware)●Bluetooth Bluetooth, EDGE, 3G, and WiFi (hardware dependent)●Camera, GPS, compass, and accelerometer (hardware dependent)●Rich development environment including a device emulator, debugger,memory and performance analysis charts, and the Eclipse integrateddevelopment environment plug-insApplicationsA core Android application package together with the release of the application package, including email client, SMS short messaging program, calendar, maps, browser, contact management procedures. A ll applications are written using JA V A.Android Application Framework Developers have full access to core applicationsused by the API framework. The application framework designed to simplify the reuse of software components; any application can publish its functional blocks and any other applications can use the function block its release (but must follow the framework of security restrictions). Reuse mechanism allows the application form can be user replaced.All of the following applications by the composition of a range of services and systems, including:●an expanded view (Views) can be used to build applications, including a list of(lists), grid (grids), text boxes (text boxes), buttons (buttons), and even an embeddable web browser.●Content Manager (Content Providers) allows applications to access data fromanother application program (such as the contact database), or to share their own data.● A resource manager (Resource Manager) to provide access to non-coderesources, such as local strings, graphics, and hierarchical file (layout files).● A notification manager (Notification Manager) allows applications to customersin the status bar display notification information.●An activity class Manager (Activity Manager) to manage the application lifecycle and provides common navigation rollback feature.Ordering the systemOrdering the system information using automated software tools to achieve la carte, side dishes, stir fry vegetables to the transfer of all management processes; completion point, the computer management menu, point the menu and the kitchen, front-end checkout synchronization print; achieved without the menu paper-based operation; backstage manager of inquiry; warehouse inventory management and so on.In addition, ordering the system can also effectively manage customer data, archiving and future reference, put an end to the restaurant "leakage List", "run list" phenomenon; help restaurants using computer data processing capability and powerful ability to process optimization to achieve automated management, streamline workflow restaurant, reduce waste and man-made phenomenon of management oversight, re-optimal allocation of corporate resources, the operating costs to a minimum.Powerful addition to ordering the system to support the general application of stand-alone and LAN in addition to support head office / branch of multi-level framework used for remote network using the POS system to achieve front store sales cashier, sales of small-ticket instantly print sales day-end, reporting sales data and receive information of new features dishes.There are three currently ordering the system to achieve mode:First, the touch screen a la carte model: It uses the currently most popular touch-computer ordering process to achieve that members can to order the software screen prompts, simply click on the screen with your fingers can complete the entire ordering process and convenient This model applies to the practice of rich dishes and large restaurants, restaurants, and restaurant, etc..Second,the wireless PDA ordering mode: it uses a wireless WiFi technology, a la carte interface by PDA display, use touch pen to complete the ordering process, virtually anywhere, anytime to order real-time response, this model is more suitable for dishes and practices simple restaurant, features a restaurant and special mood of senior restaurants.Third, the wireless ordering Po mode: it uses the ISM band, can be a floor or other obstruction in the case of seamless coverage up to 10 meters away, while the signal remained stable, which is the ratio of the wireless PDA ordering model's greatest strength, this model applies to simple dishes and practices and other requirements with fewer fast food restaurants, pot shops.中文翻译：无线局域网为何使用无线局域网络？对于局域网络管理主要工作之一，对于铺设电缆或是检查电缆是否断线这种耗时的工作，很容易令人烦躁，也不容易在短时间内找出断线所在。

Android应用程序API中英文对照外文翻译文献中英文资料对照外文翻译Android API级别当你开发你的Android应用程序时，了解该平台API变更管理的基本方法和概念是很有帮助的。

同样的，知道API级别标识以及该标识如何保障你的应用与实际硬件设备相兼容对于开发及后续的发布、维护都是有益的。

本节内容告诉你API级别的知识，以及它如何影响你开发和使用的应用。

关于如何使用“以API级别进行过滤”来使用API参考手册，从本文末尾的文档过滤(Filtering the documentation)中可以得到更多信息。

API级别是什么？API级别是一个整数值，它唯一标识了一个具体版本的Android 平台，及其框架的API的版本。

Android平台提供了一套框架API，使得应用程序可以与系统底层进行交互。

该框架API由以下模块组成：一组核心的包和类清单(manifest)文件的XML元素和属性声明资源文件的XML元素和属性声明及访问形式各类意图(Intents)应用程序可以请求的各类授权，以及系统中包含的授权执行每个Android平台的后续版本会包括它提供的更新的Android应用程序框架的API。

该框架的API的更新设计，使高版本的API与早期版本兼容。

也就是说，在新版本API中大多数都是新增功能，和引进新的或替代的功能。

作为API的部分升级，老的替换的部分已过时，但不会从新版本中删除，使得已有的应用程序仍然可以使用它们。

在极少数情况下，旧版本API的部分可能被修改或删除，通常这种变化是为了保障API的稳定性及应用程序或系统的安全。

所有其他早期版本的API将不做修改的保留。

一个Android平台提供的框架API，被指定一个整数标识符，称为“API级别”。

每一个版本的Android平台只支持有一个API级别，虽然该支持是隐含地包括了所有早期的API级别（一直到API级别1级）。

Android平台的最初版本提供的框架API级别是1级，随后的版本依次递增。

外文文献-Android Application Fundamentals安卓应用基础毕业设计外文文献原文及译文Android Application Fundamentals安卓应用基础学生姓名: 学号:计算机系系别:网络工程专业:指导教师:2015年 5 月中北大学信息商务学院2015届毕业设计外文文献原文及译文Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDK tools compile the code—along with any data and resource files—into an Android package,an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application.Once installed on a device, each Android application lives in its own security sandbox:, The Android operating system is a multi-user Linux system in which eachapplication is a different user., By default, the system assigns each application a unique Linuxuser ID (the ID isused only by the system and is unknown to the application). The system setspermissions for all the files in an application so that only theuser ID assigned tothat application can access them., Each process has its own virtual machine (VM), so an application's code runs inisolation from other applications., By default, every application runs in its own Linux process.Android starts theprocess when any of the application's components need to be executed, then shutsdown the process when it's no longer needed or when the system must recovermemory for other applications.In this way, the Android system implements the principle of least privilege. That is,each application, by default, has access only to the components that it requires to do its work and no more. This creates a very secure environment in which an application cannot access parts of the systemfor which it is not given permission.However, there are ways for an application to share data with other applications and for an application to access system services: , It's possible to arrange for two applications to share the same Linux user ID, inwhich case they are able to access each other's files. To conserve system resources,中北大学信息商务学院2015届毕业设计外文文献原文及译文applications with the same user ID can also arrange to run in the same Linuxprocess and share the same VM (the applications must also be signed with thesame certificate)., An application can request permission to access device data such as the user'scontacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, andmore. All application permissions must be granted by the user at install time. That covers the basics regarding how an Android application exists within the system. The rest of this document introduces you to:, The core framework components that define your application., The manifest file in which you declare components and required device featuresfor your application., Resources that are separate from the application code and allow your applicationto gracefully optimize its behavior for a variety of device configurations.Application ComponentsApplication components are the essential building blocks of an Android application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each one exists as its own entity and plays a specific role—each one is a unique buildingblock that helps define your application's overall behavior.There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.Here are the four types of application components:ActivitiesAn activity represents a single screen with a user interface. For example, an emailapplication might have one activity that shows a list of new emails, another activity中北大学信息商务学院2015届毕业设计外文文献原文及译文to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experiencein the email application, each one is independent of the others. As such, a different application can start any one of these activities (if the email application allows it). For example, a camera application canstart the activity in the email application that composes new mail, in order for the user to share a picture.An activity is implemented as a subclass of Activity and you canlearn more about it in the Activities developer guide.ServicesA service is a component that runs in the background to performlong-running operations or to perform work for remote processes. A service does not provide a user interface. For example, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. Another component, such as anactivity, can start the service and let it run or bind to it in order to interact with it. A service is implemented as a subclass of Service and you can learn more about it in the Services developer guide.Content providersA content provider manages a shared set of application data. You can store the data in the file system, an SQLite database, on the web, orany other persistent storage location your application can access. Through the content provider, other applications can query or evenmodify the data (if the content provider allows it). For example, the Android system provides a content provider that manages the user'scontact information. As such, any application with the properpermissions can query part of the content provider (such as ContactsContract.Data) to read and write information about a particular person.Content providers are also useful for reading and writing data thatis private to your中北大学信息商务学院2015届毕业设计外文文献原文及译文application and not shared. For example, the Note Pad sample application uses acontent provider to save notes.A content provider is implemented as a subclass of ContentProvider and mustimplement a standard set of APIs that enable other applications to performtransactions. For more information, see the Content Providers developer guide. Broadcast receiversA broadcast receiver is a component that responds to system-wide broadcastannouncements. Many broadcasts originate from the system—for example, abroadcast announcing that the screen has turned off, the battery is low, or a picturewas captured. Applications can also initiate broadcasts—for example, to let otherapplications know that some data has been downloaded to the device and isavailable for them to use. Although broadcast receivers don'tdisplay a userinterface, they may create a status bar notification to alert theuser when a broadcastevent occurs. More commonly, though, a broadcast receiver is just a "gateway" toother components and is intended to do a very minimal amount of work. Forinstance, it might initiate a service to perform some work based on the event.A broadcast receiver is implemented as a subclass of BroadcastReceiver and eachbroadcast is delivered as an Intent object. For more information,seetheBroadcastReceiver class.A unique aspect of the Android system design is that any application can start another application’s component. For example, if you want the user to capture a photo with the device camera, there's probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You don't need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera applicationthat captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application.中北大学信息商务学院2015届毕业设计外文文献原文及译文When the system starts a component, it starts the process for that application (if it's not already running) and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your application's process. Therefore, unlike applications on most other systems, Android applications don't have a single entry point (there's no main() function, for example).Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies your intent to start a particular component. The system then activates the component for you.Activating ComponentsThree of the four component types—activities, services, and broadcast receivers—areactivated by an asynchronous message called an intent. Intents bind individual componentsto each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another.An intent is created with an Intent object, which defines a message to activate either a specific component or a specific type of component—an intent can be either explicit orimplicit, respectively.For activities and services, an intent defines the action to perform (for example, to "view" or "send" something) and may specify the URI of the data to act on (among other things that the component being started might need to know). For example, an intent might convey a request for an activity to show an image or to open a web page. In some cases, you can start an activity to receive a result, in which case, the activity also returns the result in an Intent (for example, you can issue an intent to let the user pick a personal中北大学信息商务学院2015届毕业设计外文文献原文及译文contact and have it returned to you—the return intent includes a URI pointing to thechosen contact).For broadcast receivers, the intent simply defines the announcement being broadcast (for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low").The other component type, content provider, is not activated by intents. Rather, it is activated when targeted by a request from a ContentResolver. The content resolver handles all direct transactions with the content provider so that the component that's performing transactions with the provider doesn't need to and instead calls methods on the ContentResolver object. This leaves a layer of abstraction between the content provider and the component requesting information (for security).There are separate methods for activating each type of component: , You can start an activity (or give it something new to do) by passingan Intent to startActivity() or startActivityForResult() (when you want the activityto return a result)., You can start a service (or give new instructions to an ongoing service) by passingan Intent to startService(). Or you can bind to the service by passingan Intent tobindService()., You can initiate a broadcast by passing an Intent to methodslike sendBroadcast(), sendOrderedBroadcast(), orsendStickyBroadcast()., You can perform a query to a content provider by calling query()ona ContentResolver.For more information about using intents, see the Intents and Intent Filters document. More information about activating specific components is also provided in the following documents: Activities, Services, BroadcastReceiver and Content Providers.Declaring components中北大学信息商务学院2015届毕业设计外文文献原文及译文The primary task of the manifest is to inform the system about the application's components. For example, a manifest file can declare an activity as follows: <?xml version="1.0" encoding="utf-8"?> <manifest ... ><application android:icon="@drawable/app_icon.png" ... ><activity android:name="com.example.project.ExampleActivity"android:label="@string/example_label" ... ></activity>...</application></manifest>In the <application> element, the android:icon attribute points to resources for an icon that identifies the application.In the <activity> element, the android:name attribute specifies the fully qualified class name of the Activity subclass and theandroid:label attributes specifies a string to use as the user-visible label for the activity.You must declare all application components this way:, <activity> elements for activities, <service> elements for services, <receiver> elements for broadcast receivers, <provider> elements for content providersActivities, services, and content providers that you include in your source but do not declare in the manifest are not visible to the system and, consequently, can never run. However, broadcast receivers can be either declared in the manifest or created dynamically in code (as BroadcastReceiver objects) and registered with the system by calling registerReceiver().中北大学信息商务学院2015届毕业设计外文文献原文及译文Declaring component capabilitiesAs discussed above, in Activating Components, you can use an Intent to start activities, services, and broadcast receivers. You can do so by explicitly naming the target component (using the component class name) in the intent. However, the real power of intents lies in the concept of intent actions. With intent actions, you simply describe the type of action you want to perform (and optionally, the data upon which you’d like to perform the action)and allow the system to find a component on the device that can perform the action and start it. If there are multiple components that can perform the action described by the intent, then the user selects which one to use.The way the system identifies the components that can respond to an intent is by comparing the intent received to the intent filters provided in the manifest file of otherapplications on the device.When you declare a component in your application's manifest, you can optionally include intent filters that declare the capabilities of the component so it can respond to intents from other applications. You can declare an intent filter for your component by adding an <intent-filter> element as a child of the component's declaration element.For example, an email application with an activity for composing a new email might declare an intent filter in its manifest entry to respond to "send" intents (in order to send email). An activity in your application can then create an intent with the “send” action (ACTION_SEND), which the system matches to the email application’s “send” activityand launches it when you invoke the intent with startActivity().For more about creating intent filters, see the Intents and Intent Filters document.Declaring application requirementsThere are a variety of devices powered by Android and not all of them provide the same features and capabilities. In order to prevent your application from being installed on中北大学信息商务学院2015届毕业设计外文文献原文及译文devices that lack features needed by your application, it'simportant that you clearly define a profile for the types of devices your application supports by declaring device and software requirements in your manifest file. Most of these declarations are informational only and the system does not read them, but external services such as Google Play do read them in order to provide filtering for users when they search for applications from their device.For example, if your application requires a camera and uses APIs introduced in Android 2.1 (API Level 7), you should declare these as requirements in your manifest file. That way, devices that do not have a camera and have an Android version lower than 2.1cannot install your application from Google Play.However, you can also declare that your application uses the camera, but does not require it. In that case, your application must perform a check at runtime to determine if the device has a camera and disable any features that use the camera if one is not available.Here are some of the important device characteristics that youshould consider as you design and develop your application: Screen size and densityIn order to categorize devices by their screen type, Android defines twocharacteristics for each device: screen size (the physical dimensions of the screen)and screen density (the physical density of the pixels on the screen, or dpi—dotsper inch). To simplify all the different types of screen configurations, the Androidsystem generalizes them into select groups that make them easier to target.The screen sizes are: small, normal, large, and extra large.The screen densities are: low density, medium density, high density, and extra highdensity.中北大学信息商务学院2015届毕业设计外文文献原文及译文By default, your application is compatible with all screen sizes and densities, because the Android system makes the appropriate adjustments to your UI layout and image resources. However, you should create specialized layouts for certain screen sizes and provide specialized images for certain densities, using alternative layout resources, and by declaring in your manifest exactly which screen sizes your application supports with the <supports-screens> element.For more information, see the Supporting Multiple Screens document.Input configurationsMany devices provide a different type of user input mechanism, suchas a hardware keyboard, a trackball, or a five-way navigation pad. If your application requires a particular kind of input hardware, then you should declare it in your manifest with the <uses-configuration> element.However, it is rare that an application should require a certain input configuration.Device featuresThere are many hardware and software features that may or may not exist on a given Android-powered device, such as a camera, a light sensor, bluetooth, a certain version of OpenGL, or the fidelity of the touchscreen. You should never assume that a certain feature is available on all Android-powered devices (other than the availability of the standard Android library), so you should declare any features used by your application with the <uses-feature> element.Platform VersionDifferent Android-powered devices often run different versions ofthe Android platform, such as Android 1.6 or Android 2.3. Each successive version often includes additional APIs not available in the previous version. In order to indicate which set of APIs are available, each platform version specifies an API Level (for example, Android 1.0 is API Level 1 and Android 2.3 is API Level 9). If you use any APIs that were added to the platform after version 1.0, you should declare the 中北大学信息商务学院2015届毕业设计外文文献原文及译文minimum API Level in which those APIs were introduced usingthe <uses-sdk> element.It's important that you declare all such requirements for your application, because, when you distribute your application on Google Play, the store uses these declarations to filter which applications areavailable on each device. As such, your application should be available only to devices that meet all your application requirements.For more information about how Google Play filters applications based on these (and other) requirements, see the Filters on Google Play document.Application ResourcesAn Android application is composed of more than just code—it requires resources thatare separate from the source code, such as images, audio files, and anything relating to the visual presentation of the application. For example, you should define animations, menus, styles, colors, and the layout of activity user interfaces with XML files. Using application resources makes it easy to update various characteristics of your application without modifying code and—by providing sets of alternative resources—enables you to optimizeyour application for a variety of device configurations (such as different languages and screen sizes).For every resource that you include in your Android project, the SDK build tools define a unique integer ID, which you can use to reference the resource from your application code or from other resources defined in XML. For example, if your application contains an image file named logo.png (saved in the res/drawable/ directory), the SDK tools generate a resource ID named R.drawable.logo, which you can use to reference the image and insert it in your user interface.One of the most important aspects of providing resources separate from your source code is the ability for you to provide alternative resources for different device configurations. For example, by defining UI strings in XML, you can translate the strings中北大学信息商务学院2015届毕业设计外文文献原文及译文into other languages and save those strings in separate files. Then, based on a language qualifier that you append to the resourcedirectory's name (suchas res/values-fr/ for French string values) and the user's language setting, the Android system applies the appropriate language strings to your UI.Android supports many different qualifiers for your alternative resources. Thequalifier is a short string that you include in the name of your resource directories in order to define the device configuration for which those resources should be used. As another example, you should often create different layouts for your activities, depending on the device's screen orientation and size. For example, when the device screen is in portrait orientation (tall), you might want a layout with buttons to be vertical, but when the screen is in landscape orientation (wide), the buttons should be aligned horizontally. To change the layout depending on the orientation, you can define two different layouts and apply the appropriate qualifier to each layout's directory name. Then,the system automatically applies the appropriate layout depending on the current device orientation.For more about the different kinds of resources you can include in your application and how to create alternative resources for various device configurations, see theApplication Resources developer guide.中北大学信息商务学院2015届毕业设计外文文献原文及译文Android Application Fundamentals安卓应用基础在Java编程语言编写的Android应用程序的Android的SDK工具编译代码以及与任何数据和到一个Android的包，一个归档文件档案资源的.apk后缀，所有的在一个单一的代码.apk文件被认为是一个应用程序，是Android的文件，供电设备来安装应用程序。

本科毕业设计（论文）外文参考文献译文及原文学院信息工程学院专业测控技术与仪器（光机电一体化方向) 年级班别 2011级（1）班学号学生姓名指导教师2015年 6 月目录1应用程序基础 (1)1.1应用程序组件 (1)1.2激活组件：intent (3)1.3 关闭组件 (4)1.4manifest文件 (5)1.5Intent过滤器 (6)1.6基于XML的布局 (7)1Application Fundamentals (8)1.1 Application Components (8)1.2Activating components:intent (11)1.3 Shutting down components (12)1.4 The manifest file (13)1.5Intent filters (14)1.6XML-Based Layout (15)1 应用程序基础Android应用程序使用Java编程语言开发。

aapt工具把编译后的Java代码连同应用程序所需的其他数据和资源文件一起打包到一个Android包文件中，这个文件使用.apk作为扩展名。

此文件是分发并安装应用程序到移动设备的载体；是用户下载到他们的设备的文件。

单一.apk文件中的所有代码被认为是一个应用程序。

从多个角度来看，每个Android应用程序都存在于它自己的世界之中：1 默认情况下，每个应用程序均运行于它自己的Linux进程中。

当应用程序中的任何代码需要被执行时，Android启动此进程，而当不再需要此进程并且其它应用程序又请求系统资源时，则就关闭了这个进程。

2 每个进程都有其独有的虚拟机（VM），所以应用程序代码与所有其它应用程序代码是隔离运行的。

3 默认情况下，每个应用程序均被赋予一个唯一的Linux用户ID，并加以权限设置，使得应用程序的文件仅对此用户及此应用程序可见——尽管也有其它的方法使得这些文件同样能为其他应用程序所访问。

Android Application FundamentalsAndroid applications are written in the Java programming language. The Android SDKtools compile the code—along with any data and resource files—into an Android package,an archive file with an .apk suffix. All the code in a single .apk file is considered to be one application and is the file that Android-powered devices use to install the application.Once installed on a device, each Android application lives in its own security sandbox:The Android operating system is a multi-user Linux system in which each applicationis a different user.By default, the system assigns each application a unique Linux user ID (the ID is used onlyby the system and is unknown to the application). The system sets permissions for all the files in an application so that only the user ID assigned to that application can access them.Each process has its own virtual machine (VM), so an application's code runs in isolation from other applications.By default, every application runs in its own Linux process. Android starts the process when any of the application's components need to be executed, then shuts down the process when it's no longer needed or when the system must recover memory for other applications.In this way, the Android system implements theprinciple of least privilege . That is, each application, by default, has access only to the components that it requires to do its work andno more. This creates a very secure environment in which an application cannot accessparts of the system for which it is not given permission.However, there are ways for an application to share data with other applications andfor an application to access system services:It's possible to arrange for two applications to share the same Linux user ID, in whichcase they are able to access each other's files. To conserve system resources, applications with the same user ID can also arrange to run in the same Linux process and share the same VM (the applications must also be signed with the same certificate).An application can request permission to access device data such as the user's contacts, SMS messages, the mountable storage (SD card), camera, Bluetooth, and more. All application permissions must be granted by the user at install time.That covers the basics regarding how an Android application exists within the system.The rest of this document introduces you to:1、The core framework components that define your application.2、The manifest file in which you declare components and required device features for your application.3、Resources that are separate from the application code and allow your application to gracefully optimize its behavior for a variety of device configurations.Application ComponentsApplication components are the essential building blocks of an Android application. Each component is a different point through which the system can enter your application. Not all components are actual entry points for the user and some depend on each other, but each one exists as its own entity and plays a specific role— each one is a unique building block that helps define your application's overall behavior.There are four different types of application components. Each type serves a distinct purpose and has a distinct lifecycle that defines how the component is created and destroyed.Here are the four types of application components:ActivitiesAn activity represents a single screen with a user interface. For example, an email application might have one activity that shows a list of new emails, another activity to compose an email, and another activity for reading emails. Although the activities work together to form a cohesive user experience in the email application, each one is independent of the others. As such, a different application can start any one of these activities (if the email application allows it). For example, a camera application can start the activity in the email application that composes new mail, in order for the user to share a picture.An activity is implemented as a subclass ofActivity and you can learn more about it inthe Activities developer guide.ServicesA service is a component that runs in the background to perform long-running operationsor to perform work for remote processes.A service does not provide a user interface. Forexample, a service might play music in the background while the user is in a different application, or it might fetch data over the network without blocking user interaction with an activity. Another component, such as an activity, can start the service and let it run or bind toit in order to interact with it.A service is implemented as a subclass of Service and you can learn more about it inthe Services developer guide.Content providersA content provider manages a shared set of application data. You can store the data in the file system, an SQLite database,on the web, or any other persistent storage location your application can access. Through the content provider, other applications can query or even modify the data (if the content provider allows it). For example, the Android system providesa content provider that manages the user's contact information. As such, any application with the proper permissions can query part of the content provider (such as ) to read and write information about a particular person.Content providers are also useful for reading and writing data that is private to your application and not shared. For example, the Note Pad sample application uses a content provider to save notes.A content provider is implemented as a subclass of ContentProvider and must implementa standard set of APIs that enable other applications to perform transactions. For more information, see the Content Providers developer guide.Broadcast receiversA broadcast receiver is a component that responds to system-wide broadcast announcements. Many broadcasts originate from the system—for example, a broadcast announcing that the screen has turned off, the battery is low, or a picture was captured. Applications can also initiate broadcasts—for example, to let other applications know that some data has been downloaded to the device and is available for them to use. Although broadcast receivers don't display a user interface, they may create a status bar notification to alert the user when a broadcast event occurs. More commonly, though, a broadcast receiver is just a "gateway" to other components and is intended to do a very minimal amount of work. For instance, it might initiate a service to perform some work based on the event.A broadcast receiver is implemented as a subclass of BroadcastReceiver and each broadcast is delivered as an Intent object. For more information, seethe BroadcastReceiver class.A unique aspect of the Android system design is that any application can start another application ’ s component. For example, if youtthewanuser to capture a photo with the device camera, there's probably another application that does that and your application can use it, instead of developing an activity to capture a photo yourself. You don't need to incorporate or even link to the code from the camera application. Instead, you can simply start the activity in the camera application that captures a photo. When complete, the photo is even returned to your application so you can use it. To the user, it seems as if the camera is actually a part of your application.When the system starts a component, it starts the process for that application (if it's not already running) and instantiates the classes needed for the component. For example, if your application starts the activity in the camera application that captures a photo, that activity runs in the process that belongs to the camera application, not in your application's process. Therefore, unlike applications on most other systems, Android applications don't have a single entry point (there's nomain() function, for example).Because the system runs each application in a separate process with file permissions that restrict access to other applications, your application cannot directly activate a component from another application. The Android system, however, can. So, to activate a component in another application, you must deliver a message to the system that specifies yourintent to start a particular component. The system then activates the component for you.Activating ComponentsThree of the four component types—activities, services, and broadcast receivers—are activated by an asynchronous message called anintent. Intents bind individual componentsto each other at runtime (you can think of them as the messengers that request an action from other components), whether the component belongs to your application or another.An intent is created with anIntent object, which defines a message to activate either a specific component or a specifictype of component—an intent can be either explicit or implicit, respectively.For activities and services, an intent defines the action to perform (for example, to "view" or "send" something) and may specify the URI of the data to act on (among other things that the component being started might need to know). For example, an intent might convey a request for an activity to show an image or to open a web page. In some cases, you can start an activity to receive a result, in which case, the activity also returns the result in an Intent (for example, you can issue an intent to let the user pick a personal contact and have it returned to you—the return intent includes a URI pointing to the chosen contact).For broadcast receivers, the intent simply defines the announcement being broadcast (for example, a broadcast to indicate the device battery is low includes only a known action string that indicates "battery is low").The other component type, content provider, is not activated by intents. Rather, it is activated when targeted by a request froma ContentResolver. The content resolver handlesall direct transactions with the content provider so that the component that's performing transactions with the provider doesn't need to and instead calls methods onthe ContentResolverobject. This leaves a layer of abstraction between the content providerand the component requesting information (for security).There are separate methods for activating each type of component:You can start an activity (or give it something new to do) by passingan Intent to startActivity() or startActivityForResult()(when you want the activity to return a result).You can start a service (or give new instructions to an ongoing service) by passingan Intent to startService() . Or you can bind to the service by passingan Intent to bindService() .You can initiate a broadcast by passing an Intent to methodslike sendBroadcast(), sendOrderedBroadcast(), or sendStickyBroadcast().You can perform a query to a content provider by calling query() on a ContentResolver .For more information about using intents, see the Intents and Intent Filters document.More information about activating specific components is also provided in the following documents: Activities, Services, BroadcastReceiver and Content Providers .Declaring componentsThe primary task of the manifest is to inform the system about the application's components. For example, a manifest file can declare an activity as follows:<?xml version="1.0" encoding="utf-8"?><manifest ... ><application android:icon="@drawable/app_icon.png" ... > <activityandroid:name="com.example.project.ExampleActivity"android:label="@string/example_label" ... ></activity>...</application></manifest>In the <application> element, the android:icon attribute points to resources for anicon that identifies the application.In the <activity> element, the android:nameattribute specifies the fully qualified class name of the Activity subclass and the android:labelattributes specifies a string to use as the user-visible label for the activity.You must declare all application components this way:1、<activity > elements for activities2、<service> elements for services3、<receiver > elements for broadcast receivers4、<provider > elements for content providersActivities, services, and content providers that you include in your source but do not declare in the manifest are not visible to the system and, consequently, can never run. However, broadcast receivers can be either declared in the manifest or created dynamically in code (asBroadcastReceiverobjects) and registered with the system by calling registerReceiver().Declaring component capabilitiesAndroid外文文件翻译——As discussed above, in Activating Components, you can usean Intent to start activities, services, and broadcast receivers. You can do so by explicitly naming the target component(using the component class name) in the intent. However, the real power of intents lies in the concept of intent actions. With intent actions, you simply describe the type of action youwant to perform (and optionally, the data upon which you like to perform’d the action) andallow the system to find a component on the device that can perform the action and start it. Ifthere are multiple components that can perform the action described by the intent, then theuser selects which one to use.The way the system identifies the components that can respond to an intent isby comparing the intent received to theintent filters provided in the manifest file ofother applications on the device.When you declare a component in your application's manifest, you can optionally includeintent filters that declare the capabilities of the component so it can respond to intents fromother applications. You can declare an intentfilter for your component by adding an <intent-filter > element as a child of the component's declaration element.For example, an email application with an activity for composing a new email mightdeclare an intent filter in its manifest entry to respond to "send" intents (in order to sendemail). An activity in your application can then create an intent with the“ send (ACTION_SEND), which the system matches to the email application’ s“ send” activit launches it when you invoke the intent withstartActivity() .For more about creating intent filters, see theIntents and Intent Filtersdocument.Declaring application requirementsThere are a variety of devices powered by Android and not all of them provide the samefeatures and capabilities. In order to prevent your application from being installed on devicesthat lack features needed by your application, it's important that you clearly define a profile forthe types of devices your application supports by declaring device and software requirementsin your manifest file. Most of these declarations are informational only and the system doesnot read them, but external services such as Google Play do read them in order to providefiltering for users when they search for applications from their device.For example, if your application requires a camera and uses APIs introduced in Android 2.1 (API Level 7), you should declare these as requirements in your manifest file. That way, devices that donot have a camera and have an Android versionlower than 2.1 cannot install your application from Google Play.However, you can also declare that your application uses the camera, but doesnot require it. In that case, your application must perform a check at runtime to determine if the device has a camera and disable any features that use the camera if one is not available.Here are some of the important device characteristics that you should consider asyou design and develop your application:Screen size and densityIn order to categorize devices by their screen type, Android defines two characteristics for each device: screen size (the physical dimensions of the screen) and screen density (the physical density of the pixels on the screen, or dpi—dots per inch). To simplify all the different types of screen configurations, the Android system generalizes them into select groups that make them easier to target.The screen sizes are: small, normal, large, and extra large.The screen densities are: low density, medium density, high density, and extra high density.By default, your application is compatible with all screen sizes and densities, because the Android system makes the appropriate adjustments to your UI layout and image resources. However, you should create specialized layouts for certain screen sizes and provide specialized images for certain densities, using alternative layout resources, and by declaring in your manifest exactly which screen sizes your application supportswith the <supports-screens> element.For more information, see the Supporting Multiple Screens document.Input configurationsMany devices provide a different type of user input mechanism, such as a hardware keyboard, a trackball, or a five-way navigation pad. If your application requires a particular kind of input hardware, then you should declare it in your manifest with the <uses-configuration> element. However, it is rare that an application should require acertain input configuration.Device featuresThere are many hardware and software features that may or may not exist on a given Android-powered device, such as a camera, a light sensor, bluetooth, a certain version of OpenGL, or the fidelity of the touchscreen. You should never assume that a certain feature is available on all Android-powered devices (other than the availability of the standard Android library), so you should declare any features used by your application withthe <uses-feature> element.Platform VersionDifferent Android-powered devices often run different versions of the Android platform, such as Android 1.6 or Android 2.3. Each successive version often includes additional APIs not available in the previous version. In order to indicate which set of APIs are available, each platform version specifies an API Level (for example, Android 1.0 is API Level 1 and Android2.3 is API Level 9). If you use any APIs that were added to the platform after version 1.0, you should declare the minimum API Level in which those APIs were introduced using the <uses-sdk> element.It's important that you declare all such requirements for your application, because, when you distribute your application on Google Play, the store uses these declarations to filter which applications are available on each device. As such, your application should be available only to devices that meet all your application requirements.For more information about how Google Play filters applications based on these(and other) requirements, see the Filters on Google Play document.Application ResourcesAn Android application is composed of more than just code— it requires resources thatare separate from the source code, such as images, audio files, and anything relating to the visual presentation of the application. For example, you should define animations, menus, styles, colors, and the layout of activity user interfaces with XML files. Using application resources makes it easy to update various characteristics of your application without modifying code and—by providing sets of alternative resources—enables you to optimizeyour application for a variety of device configurations (such as different languages and screen sizes).For every resource that you include in your Android project, the SDK build tools define a unique integer ID, which you can use to reference the resource from your application code or from other resources defined in XML. For example, if your application contains an image file named logo.png (saved in the res/drawable/ directory), the SDK tools generate a resourceID named R.drawable.logo, which you can use to reference the image and insert it in your user interface.One of the most important aspects of providing resources separate from your source code is the ability for you to provide alternative resources for different device configurations. For example, by defining UI strings in XML, you can translate the strings into other languages and save those strings in separate files. Then, based on a languagequalifier that you append to the resource directory's name (such as res/values-fr/ for French string values) and the user's language setting, the Android system applies the appropriate language strings to your UI.Android supports many different qualifiers for your alternative resources. The qualifier is a short string that you include in the name of your resource directories in order to define the device configuration for which those resources should be used. As another example, you should often create different layouts for your activities, depending on the device's screen orientation and size. For example, when the device screen is in portrait orientation (tall), you might want a layout with buttons to be vertical, but when the screen is in landscape orientation (wide), the buttons should be aligned horizontally. To change the layout depending on the orientation, you can define two different layouts and apply the appropriate qualifier to each layout's directory name. Then, the system automatically applies the appropriate layout depending on the current device orientation.For more about the different kinds of resources you can include in your applicationand how to create alternative resources for various device configurations, see theApplication Resourcesdeveloper guide.安卓应用基础在Java编程语言编写的 Android 应用程序的 Android 的 SDK 工具编译代码以及与任何数据和到一个Android 的包，一个归档文件档案资源的 .apk 后缀，所有的在一个单一的代码 .apk 文件被认为是一个应用程序，是 Android 的文件，供电设备来安装应用程序。