@Override  
public boolean dispatchKeyEvent(KeyEvent event) {  
    // TODO Auto-generated method stub  
    if (event.getAction() == KeyEvent.ACTION_DOWN  
            && event.getKeyCode() == KeyEvent.KEYCODE_BACK) {  
        //do something what you want  
        return true;//返回true，把事件消费掉，不会继续调用onBackPressed  
    }  
    return super.dispatchKeyEvent(event);  
} 

/** 
 * 模拟键盘事件方法 
 * @param keyCode 
*/  
public void actionKey(final int keyCode) {  
     new Thread () {    
                public void run () {    
                    try {    
                         Instrumentation inst=new Instrumentation();    
                         inst.sendKeyDownUpSync(keyCode);  
                    } catch(Exception e) {    
                        e.printStackTrace();                    }    
                }    
            }.start();    
        }
}