<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android" >
    <item 
        android:state_checked="true"
        android:state_enabled="true" 
        android:drawable="@drawable/btn_check_on" />
   <item 
       android:state_checked="false"
       android:state_enabled="true"
       android:drawable="@drawable/btn_check_off" />
</selector>