添加发送键值按钮

在android 4.2.2中视频播放器当中看到有虚拟音量键，对于这种发送键值的按钮，看看源码怎么实现：

private void sendKeyIntent(int keycode){
  final int keyCode = keycode;
  // to avoid deadlock, start a thread to perform operations
        Thread sendKeyDelay = new Thread(){  
            public void run() {
                try {
                    int count = 1;
                    if(keyCode == KeyEvent.KEYCODE_BACK)
                        count = 2;
                   
                    IWindowManager wm = IWindowManager.Stub.asInterface(ServiceManager.getService("window"));//得到WindowManager的实例对象；
                    for(int i = 0; i < count; i++){
                        Thread.sleep(100);
                        long now = SystemClock.uptimeMillis();//得到系统当前时间
                        if(!mOnPause) {
                         KeyEvent keyDown = new KeyEvent(now, now, KeyEvent.ACTION_DOWN, keyCode, 0);//把虚拟音量按键包装进KeyEvnet对象
             InputManager.getInstance().injectInputEvent(keyDown, InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);//获得InputManager实例并发送keycode
//                         wm.injectKeyEvent(keyDown, false);  
            
                         KeyEvent keyUp = new KeyEvent(now, now, KeyEvent.ACTION_UP, keyCode, 0);
                         InputManager.getInstance().injectInputEvent(keyUp, InputManager.INJECT_INPUT_EVENT_MODE_ASYNC);  
//                         wm.injectKeyEvent(keyUp, false);
                        }
                    } 
                } catch (InterruptedException e) {
                    e.printStackTrace();  
                }  
            }  
        };
        sendKeyDelay.start();//线程开始
    }