LinearLayout按下(pressed)或获取焦点（focused)时背景设置不同颜色或图片

<LinearLayout   
    xmlns:android="http://schemas.android.com/apk/res/android"  
    android:id="@+id/myview"  
    android:orientation="horizontal"  
    android:layout_width="fill_parent"  
    android:layout_height="wrap_content"  
    android:gravity="top"  
    android:background="@drawable/myDrawable"  
    android:clickable="true" >  
</LinearLayout>