android - Handler postDelayed 无效。

Question

        mHandler.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        mHandler.removeCallbacksAndMessages(null);
                    }
                }, 500);
                
                
                
                 mHandler.removeCallbacksAndMessages(null); 用来移除所有消息，
                 
                 但是用handler.postdelayed 无效，
                 是用TimerTask 或者 Thread  来控制时 是可以生效的。
                 
                请问因为什么原因导致无效的呢？
                
              

Answer 1

What is the function of removeCallbacksAndMessages(null)?

If the parameter is null, all Callbacks and Messages will be cleared.
You are looking at the source code. The constructor of Message is empty and what is 0. It has not been executed yet and will be deleted.

Answer 2

Excuse me, why is it invalid? Is mHandler.removeCallbacksAndMessages(null); not executed?

Answer 3

It feels a bit strange to remove my own runnable after a delay of 500.
You can try this

mHandler = new Handler(){
   handleMessage(Message msg){
    switch(msg.what){
    case REMOVE:
       removeCallbacksAndMessages(null);
    }
   }
}
....
mHandler.sendEmptyMessageDelayed(REMOVE, 500);