Android中的Drawable资源—— StateListDrawable

这种使用xml来定义图片的方式在buttion中经常使用，它会根据状态来显示不同的图片资源。

存放位置：
res/drawable/

使用方式：
在Java文件中：R.drawable.filename

例如：

Resources res = getResources();
Drawable drawable = res.getDrawable(R.drawable.myimage);

在xml布局文件中：@[package:]drawable/filename

例如：

<Button  android:layout_height="wrap_content" android:layout_width="wrap_content" android:background="@drawable/myninepatch" />

语法：

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android"
    android:constantSize=["true" | "false"]
    android:dither=["true" | "false"]
    android:variablePadding=["true" | "false"] >
    <item
        android:drawable="@[package:]drawable/drawable_resource"
        android:state_pressed=["true" | "false"]
        android:state_focused=["true" | "false"]
        android:state_hovered=["true" | "false"]
        android:state_selected=["true" | "false"]
        android:state_checkable=["true" | "false"]
        android:state_checked=["true" | "false"]
        android:state_enabled=["true" | "false"]
        android:state_activated=["true" | "false"]
        android:state_window_focused=["true" | "false"] />
</selector>

例如：

<?xml version="1.0" encoding="utf-8" ?>     
<selector xmlns:android="http://schemas.android.com/apk/res/android">   
  <!-- 触摸时并且当前窗口处于交互状态 -->    
  <item android:state_pressed="true" android:state_window_focused="true" android:drawable= "@drawable/pic1" />  
  <!-- 触摸时并且没有获得焦点状态 -->    
  <item android:state_pressed="true" android:state_focused="false" android:drawable="@drawable/pic2" />    
  <!--选中时的图片背景-->    
  <item android:state_selected="true" android:drawable="@drawable/pic3" />     
  <!--获得焦点时的图片背景-->    
  <item android:state_focused="true" android:drawable="@drawable/pic4" />    
  <!-- 窗口没有处于交互时的背景图片 -->    
  <item android:drawable="@drawable/pic5" />   
</selector>  

<Button  android:layout_height="wrap_content" android:layout_width="wrap_content" android:background="@drawable/button" />

另外，需要说的是，上面定义的这个xml会被相应的解析为StateListDrawable对象，所以我们也可以使用代码来进行实现。

//初始化一个空对象  
StateListDrawable stalistDrawable = new StateListDrawable(); 
//获取对应的属性值 Android框架自带的属性 attr  
int pressed = android.R.attr.state_pressed; 
int window_focused = android.R.attr.state_window_focused; 
int focused = android.R.attr.state_focused; 
int selected = android.R.attr.state_selected; 

stalistDrawable.addState(new int []{pressed , window_focused}, getResources().getDrawable(R.drawable.pic1)); 
stalistDrawable.addState(new int []{pressed , -focused}, getResources().getDrawable(R.drawable.pic2); 
stalistDrawable.addState(new int []{selected }, getResources().getDrawable(R.drawable.pic3); 
stalistDrawable.addState(new int []{focused }, getResources().getDrawable(R.drawable.pic4); 
//没有任何状态时显示的图片，我们给它设置我空集合  
stalistDrawable.addState(new int []{}, getResources().getDrawable(R.drawable.pic5); 

上面的“-”负号表示对应的属性值为false

https://developer.android.com/guide/topics/resources/drawable-resource.html#StateList

https://developer.android.com/reference/android/graphics/drawable/StateListDrawable.html

http://blog.csdn.net/qinjuning/article/details/7474827