Android 点击ImageButton时有“按下”的效果的实现

imageButton.setOnTouchListener(new OnTouchListener(){   
            @Override  
            public boolean onTouch(View v, MotionEvent event) {   
                if(event.getAction() == MotionEvent.ACTION_DOWN){   
                    //更改为按下时的背景图片   
                    v.setBackgroundResource(R.drawable.pressed);   
                }else if(event.getAction() == MotionEvent.ACTION_UP){   
                    //改为抬起时的图片   
                    v.setBackgroundResource(R.drawable.released);   
                }   
                return false;   
            }   
        });  

<?xml version="1.0" encoding="UTF-8"?>  
<selector xmlns:android="http://schemas.android.com/apk/res/android">  
  <item android:state_pressed="false" android:drawable="@drawable/button_add" />  
  <item android:state_pressed="true"  android:drawable="@drawable/button_add_pressed" />  
  <item android:state_focused="true"  android:drawable="@drawable/button_add_pressed" />  
  <item android:drawable="@drawable/button_add" />  
</selector>