使一个button无效时变灰

<selector xmlns:android="http://schemas.android.com/apk/res/android"]] >   
    <item   
    android:state_enabled="false"  
        android:drawable="@drawable/btn_red" />  
    <item   
        android:state_pressed="true"   
        android:state_enabled="true"  
        android:drawable="@drawable/btn_orange" />  
    <item   
        android:state_focused="true"   
        android:state_enabled="true"  
        android:drawable="@drawable/btn_orange" />  
    <item   
        android:state_enabled="true"  
        android:drawable="@drawable/btn_black" />  
</selector]] >

        button.setEnabled(false);