android selector的使用

<?xml version="1.0" encoding="utf-8" ?> 
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:state_window_focused="false" 
        android:drawable="@drawable/没有焦点时的图片背景" /> 
  <item android:state_focused="true" android:state_pressed="true" 
        android:drawable=
              "@drawable/非触摸模式下获得焦点并单击时的背景图片" /> 
  <item android:state_focused="false" android:state_pressed="true" 
        android:drawable="@drawable/触摸模式下单击时的背景图片" /> 
  <item android:state_selected="true" 
        android:drawable="@drawable/选中时的图片背景" /> 
  <item android:state_focused="true" 
        android:drawable="@drawable/获得焦点时的图片背景" /> 
</selector>