点击换图的实现

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="https://schemas.android.com/apk/res/android" > 
    <!-- 后边这个是android命名空间 -->
    
    <item android:state_focused="true" android:state_enabled="true" android:state_pressed="false" android:drawable="@drawable/compass" /> 
    <!-- 设置没有被按下时显示的图片 -->
    <item android:state_enabled="true" android:state_pressed="true" android:drawable="@drawable/center_bg_click" />  
    <!-- 按下时显示的图片 -->
    
    <item android:state_enabled="true" android:state_checked="true" android:drawable="@drawable/center_bg_click" />
    <item android:drawable="@drawable/compass" />
</selector><?xml version="1.0" encoding="utf-8"?>
<selector x