Drawable(3)Color State List Resource

　　注意 Color State List Resource 与 Color不同,前者是颜色状态表.根据不同状态显示不同颜色,它是State list,里面有多种颜色,后者只是一个颜色.

Color State List Resource

　　A ColorStateList is an object you can define in XML that you can apply as a color, but will actually change colors, depending on the state of the View object to which it is applied. For example, a Buttonwidget can exist in one of several different states (pressed, focused, or niether) and, using a color state list, you can provide a different color during each state.

　　You can describe the state list in an XML file. Each color is defined in an <item> element inside a single<selector> element. Each <item> uses various attributes to describe the state in which it should be used.

　　During each state change, the state list is traversed top to bottom and the first item that matches the current state will be used—the selection is not based on the "best match," but simply the first item that meets the minimum criteria of the state.

Note: If you want to provide a static color resource, use a simple Color value.

FILE LOCATION:

　　res/color/filename.xml

　　The filename will be used as the resource ID.

COMPILED RESOURCE DATATYPE:

　　Resource pointer to a ColorStateList.

RESOURCE REFERENCE:

　　In Java: R.color.filename

　　In XML: @[package:]color/filename

SYNTAX:

 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android" >
     <item
         android:color="hex_color"
         android:state_pressed=["true" | "false"]
         android:state_focused=["true" | "false"]
         android:state_selected=["true" | "false"]
         android:state_checkable=["true" | "false"]
         android:state_checked=["true" | "false"]
         android:state_enabled=["true" | "false"]
         android:state_window_focused=["true" | "false"] />
 </selector>

ELEMENTS:

<selector>

　　Required. This must be the root element. Contains one or more <item> elements.

attributes:

xmlns:android

　　String. Required. Defines the XML namespace, which must be"http://schemas.android.com/apk/res/android".

<item>

　　Defines a color to use during certain states, as described by its attributes. Must be a child of a<selector> element.

attributes:

android:color

　　　　Hexadeximal color. Required. The color is specified with an RGB value and optional alpha channel.

　　　　The value always begins with a pound (#) character and then followed by the Alpha-Red-Green-Blue information in one of the following formats:

• #RGB
• #ARGB
• #RRGGBB
• #AARRGGBB

android:state_pressed

　　Boolean. "true" if this item should be used when the object is pressed (such as when a button is touched/clicked); "false" if this item should be used in the default, non-pressed state.

android:state_focused

　　Boolean. "true" if this item should be used when the object is focused (such as when a button is highlighted using the trackball/d-pad); "false" if this item should be used in the default, non-focused state.

android:state_selected

　　Boolean. "true" if this item should be used when the object is selected (such as when a tab is opened); "false" if this item should be used when the object is not selected.

android:state_checkable

　　Boolean. "true" if this item should be used when the object is checkable; "false" if this item should be used when the object is not checkable. (Only useful if the object can transition between a checkable and non-checkable widget.)

android:state_checked

　　Boolean. "true" if this item should be used when the object is checked; "false" if it should be used when the object is un-checked.

android:state_enabled

　　Boolean. "true" if this item should be used when the object is enabled (capable of receiving touch/click events); "false" if it should be used when the object is disabled.

android:state_window_focused

　　Boolean. "true" if this item should be used when the application window has focus (the application is in the foreground), "false" if this item should be used when the application window does not have focus (for example, if the notification shade is pulled down or a dialog appears).

Note: Remember that the first item in the state list that matches the current state of the object will be applied. So if the first item in the list contains none of the state attributes above, then it will be applied every time, which is why your default value should always be last (as demonstrated in the following example).

EXAMPLE:

XML file saved at res/color/button_text.xml:

 <?xml version="1.0" encoding="utf-8"?>
 <selector xmlns:android="http://schemas.android.com/apk/res/android">
     <item android:state_pressed="true"
           android:color="#ffff0000"/> <!-- pressed -->
     <item android:state_focused="true"
           android:color="#ff0000ff"/> <!-- focused -->
     <item android:color="#ff000000"/> <!-- default -->
 </selector>

This layout XML will apply the color list to a View:

 <Button
     android:layout_width="fill_parent"
     android:layout_height="wrap_content"
     android:text="@string/button_text"
     android:textColor="@color/button_text" />