Handler 的sendEmptyMessage(int what)和sendMessage（Message msg）的区别？

最新推荐文章于 2022-12-06 03:22:22 发布

jcl490195138

最新推荐文章于 2022-12-06 03:22:22 发布

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分类专栏： Android基础知识

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本文详细解释了Android中Handler类的sendEmptyMessage与sendMessage方法的区别与联系。通过源码解析这两种消息发送方式的具体实现，并给出了实际应用场景示例。

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Handler用sendEmptyMessage(int what)发消息，其实也可以用sendMessage（Message msg）的，但两者到底有啥区别？

直接上Handler源码：

/**
* Sends a Message containing only the what value.
* 
* @return Returns true if the message was successfully placed in to the 
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessage(int what)
{
   return sendEmptyMessageDelayed(what, 0);
}

就是调用了sendEmptyMessageDelayed（）而已，下面看下这个方法：

/**
* Sends a Message containing only the what value, to be delivered
* after the specified amount of time elapses.
* @see #sendMessageDelayed(android.os.Message, long) 
* 
* @return Returns true if the message was successfully placed in to the 
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendEmptyMessageDelayed(int what, long delayMillis) {
Message msg = Message.obtain();
msg.what = what;
return sendMessageDelayed(msg, delayMillis);
}

而sendMessage（Message msg）的实现和上面一样，请看：

/**
* Pushes a message onto the end of the message queue after all pending messages
* before the current time. It will be received in {@link #handleMessage},
* in the thread attached to this handler.
* 
* @return Returns true if the message was successfully placed in to the 
* message queue. Returns false on failure, usually because the
* looper processing the message queue is exiting.
*/
public final boolean sendMessage(Message msg)
{
return sendMessageDelayed(msg, 0);
}

就是在 sendEmptyMessageDelayed中就是构建了一个Message,然后把这个Message的what设置成sendEmptyMessage方法中的What参数即可。

比如：

    private Handler handler = new Handler() {
        @Override
        public void handleMessage(Message msg) {
            ll_pb.setVisibility(View.INVISIBLE);
            if(adapter == null){
                adapter = new CallSafeAdapter(blackNumberInfos, CallSafeActivity.this);
                list_view.setAdapter(adapter);
            }else{
                adapter.notifyDataSetChanged();
            }

        }
    };

    private void initData() {
        dao = new BlackNumberDao(CallSafeActivity.this);
        //一共有多少条数据
        totalNumber = dao.getTotalNumber();
        new Thread() {
            @Override
            public void run() {


                //分批加载数据
                if (blackNumberInfos == null) {
                    blackNumberInfos = dao.findPar2(mStartIndex, maxCount);
                } else {
                    //把后面的数据。追加到blackNumberInfos集合里面。防止黑名单被覆盖
                    blackNumberInfos.addAll(dao.findPar2(mStartIndex, maxCount));
                }

                handler.sendEmptyMessage(0);
            }
        }.start();
    }

当在子线程里的耗时操作已经结束了，这是我们需要发送一个消息告诉主线程我的耗时操作已经结束了，你赶紧处理吧！