<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <!-- 无状态时 -->
  <item
    android:state_focused="false"
    android:state_selected="false"
    android:state_pressed="false"
    android:state_enabled="true"
    android:drawable="@drawable/blue" />
  <!-- 选中状态 -->
  <item
    android:state_focused="false"
    android:state_selected="true"
    android:state_pressed="false"
    android:state_enabled="true"
    android:drawable="@drawable/blue" />
  <!-- 获得焦点 -->
  <item
    android:state_focused="true"
    android:state_selected="false"
    android:state_pressed="false"
    android:state_enabled="true"
    android:drawable="@drawable/blue" />
  <!-- 按下时的状态 -->
  <item
    android:state_focused="false"
    android:state_selected="false"
    android:state_pressed="true"
    android:state_enabled="true"
    android:drawable="@drawable/blue" />
</selector>