android

View and ViewGroup[1/3]y Viewy This class represents the basic building block for user int erface components.y A View occupies a rectangular area on the screen and is r esponsible for drawing and event handling.View and ViewGroup[2/3]y ViewGroupy The ViewGroup subclass is the base class for layouts, which are invis ible containers that hold other Views (or other ViewGroups) and de fine their layout properties.y A ViewGroup is a special view that can contain other views (called c hildren.)y ViewGroup may include other views or viewgroup.y It can be existed by itselfy There are two major categories –Layout and adapterView and ViewGroup[2/3] y View HierarchyView attribute and method[1/5]y Identifier IDy Views may have an integer id associated with them.y These ids are typically assigned in the layout XML files, and are used to find specific views within the view tree.y View IDs need not be unique throughout the tree, but it is good pra ctice to ensure that they are at least unique within the part of the tree you are searching.View attribute and method[2/5] y Identifier ID<Button id="@+id/my_button"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="@string/my_button_text"/>Button myButton = (Button) findViewById(R.id.my_button);View attribute and method[3/5]y Size and Positiony The geometry of a view is that of a rectangle. A view has a location, expressed as a pair of left and top coordinates, and two dimensions, expressed as a width and a height.y The unit for location and dimensions is the pixel.y Using XML layout properties‐layout_width and layout_height or V youtParams() methody Marginy paddingy paddingTop, paddingBottom, paddingLeft, paddingRightView attribute and method[4/5]y XML attributesy android:visibility–Determining whether a screen representation of the widget.y Android:background‐A hex RGB (# FFFFFF format) to specify thebackground color of the widget.View attribute and method[5/5]y Methodsy setEnable() ‐Set the enabled state of this view.y isEnable() ‐True if this view is enabled, false otherwise.y requestFocus() ‐Call this to try to give focus to a specific view or to one of its descendants and give it a hint about what direction focus is heading.y getParent() ‐Gets the parent of this view.y findViewById() ‐Look for a child view with the given id.If this view has the given id, return this view.y getRootView() ‐Finds the topmost view in the current vi ew hierarchy.Overview[1/3]y Meaningy The word widget is a placeholder name for an object or, more specifi cally, a mechanical or other manufactured device.y In computer programming, a widget (or control) is an element of a g raphical user interface (GUI) that displays an information arrangem ent changeable by the user, such as a window or a text box.y A subclass of view, such as object and text field.y This is a component that displaying information to users or accepts input from user.y DatePicker, TimePicker, ZoomControls are derived from Viewgroup that are used like widget.Overview[2/3]y Kind of widgets ‐1Class Name DescriptionsTextView Displays text to the user and optionally allows them to edit it.EditText EditText is a thin veneer over TextView that configures itself to be editable.AutoCompleteTextView An editable text view that shows completion suggestions automatically while the user is typing.ImageView Displays an arbitrary image,such as an icon.VideoView Displays a video file.Button Represents a push‐button widget. CompoundButton A button with two states, checked and unchecked.CheckBox A checkbox is a specific type of two‐states button that can be either checked or u nchecked.RadioButton A radio button is a two‐states button that can be either checked or unchecked.Overview[3/3]y Kind of widgets ‐2Class Name DescriptionsRadioGroup This class is used to create a multiple‐exclusion scope for a set of radio buttons. ImageButton Displays a button with an image(instead of text)that can be pressed or clicked by the user. AnalogClock This widget display an analogic clock with two hands for hours and minutes.DigitalClock Like AnalogClock,but digital.Chronometer Class that implements a simple timer.ProgressBar Visual indicator of progress in some operation.DatePicker This class is a widget for selecting a date.TimePicker A view for selecting the time of day,in either24hour or AM/PM mode.The ZoomControls class displays a simple set of controls used for zooming and provides call ZoomControlsTypical widgets[1/6]y TextViewy Show Labely Including most of the features that a string of input, output, editing , formattingy android:typeface‐Typeface (normal, sans, serif, monospace) for the text.y android:textstyle‐Style (bold, italic, bolditalic) for the text.y android:textColor‐Text color.y android:text‐Text to display.Typical widgets[2/6]y EditTexty EditText is a thin veneer over TextView that configures itself to be editable.y android:autoText‐If set, specifies that this TextView has a textual input method and automatically corrects some common spelling err ors.y android:capitalize‐If set, specifies that this TextView has a textual i nput method and should automatically capitalize what the user types.y Android:digits‐If set, specifies that this TextView has a numeric input method and that these specific characters are the ones that it wi ll accept.y Android:singleLine‐Constrains the text to a single horizontally scrolling line instead of letting it wrap onto multiple lines, and advances focus instead of inserting a newline when you press the enter key.Typical widgets[3/6]y Buttony Represents a push‐button widget. Push‐buttons can be p ressed, or clicked, by the user to perform an action.Typical widgets[4/6]y Buttony CheckBoxy A checkbox is a specific type of two‐states button thatcan be either checked or unchecked.y isChecked()y setChecked(true/false) –Changes the checked state ofthis button.y toggle() ‐Change the checked state of the view to the inverse of its current stateTypical widgets[5/6]y Buttony RadioButtony A radio button is a two‐states button that can be either checked or unchecked.y Radio buttons are normally used together in a RadioGroup.y When several radio buttons live inside a radio group, checking one radio button unchecks all the others.y contrary to a CheckBox, a radio button cannot be unchecked by the user once checked.y When the radio button is unchecked, the user can press or click itto check it.Typical widgets[6/6]y Buttony ImageView and ImageButtony Displays an arbitrary image, such as an icon.y ImageView attributesy srcy maxWidth, maxHeightApplications[1/2]y Widget1DemoApplications[2/2]y Widget2Demo y Widget3DemoOverview[1/4]y Meaningy Your layout is the architecture for the user interface in an Activity.y It defines the layout structure and holds all the elements that appea r to the user.y Like all layouts, they are subclasses of ViewGroup.y The advantage to declaring your UI in XML is that it enables you to better separate the presentation of your application from the code t hat controls its behavior.Overview[2/4] y Layout HierarchyOverview[3/4]y Layout attributesy Every View and ViewGroup object supports their own variety of XM L attributes.y Some attributes are specific to a View object , but these attributes are also inherited by any View objects that may extend this class.y Some are common to all View objects, because they are inherited from the root View class.y And, other attributes are considered "layout parameters," which are attributes that describe certain layout orientations of the View objec t, as defined by that object's parent ViewGroup objet.Overview[4/4]y Typical Attributes y layout_weighty layout_gravityy layout_marginy Etc.Linear and Table Layout[1/2]y LinearLayouty LinearLayout aligns all children in a single direction —vertically or horizontally , depending on how do you define the orientation attribute. ( default value = horizontal )y LinearLayout is used frquentlyy This attribute assigns an "importance" value to a view, and allows it t o expand to fill any remaining space in the parent view.Linear and Table Layout[2/2]y TableLayouty TableLayout positions its children into rows and columns.y Subclass of LinearLayouty Attributesy TableRow defines a single row in the tabley TextView is the role of output stringy View displays a horizontal dividerAbsolute Layouty AbsoluteLayouty A layout that lets you specify exact locations (x/y coordinates) of its children.y Absolute layouts are less flexible and harder to maintain than other types of layouts without absolute positioning.RelativeLayouty RelativeLayouty RelativeLayout lets child views specify their position rela tive to the parent view or to each other (specified by ID) y Attributesy android:orientationy android:layout_widthy android:layout_heighty android:layout_abovey android:layout_belowy android:layout_alignBaseliney android:layout_alignBottomy android:layout_alignLefty android:layout_alignRighty android:layout_alignTopy android:layout_toLeftOfy android:layout_toRightOfOther Layouts y FrameLayout y All child elements of the Fra meLayout are pinned to the t op left corner of the screen; y ou cannot specify a different location for a child view. y ScrollView y Subclass of RelativeLayout y A vertically scrolling column of elements.。