public boolean onKeyDown (int keyCode, KeyEvent event)
Returns
Return true to prevent this event from being propagated further, or false to indicate that you have not handled this event and it should continue to be propagated.
返回true以防止进一步传播此事件，或返回false以指示您尚未处理此事件，应继续传播它。
即返回true表示方法执行到此。