为按钮定义selector方法如下：
1 <?xml version="1.0" encoding="utf-8"?> 2 <selector xmlns:android="http://schemas.android.com/apk/res/android"> 3 4 <item android:drawable="@drawable/red" android:state_pressed="true"></item> 5 <item android:drawable="@drawable/red" android:state_focused="true"></item> 6 <item android:drawable="@drawable/purple" android:state_window_focused="true"></item> 7 8 </selector>