Handler-线程间通信

线程通信

Handler

获取到哪个线程的Handler，就可以给这个线程发送消息。

Looper

线程间通信的桥梁。

案例

更新UI数据

动态更新Activity界面上面的数据。3s后，让界面上的数字每秒后增加1。

1. UI线程创建Handler，负责接收普通线程发送的数字增加消息并更新Activity界面。

	Handler uiHandler = null;
	
	public void initHandler(){
        uiHandler = new Handler(){
            @Override
            public void handleMessage(@NonNull Message msg) {
                Log.d(TAG, String.format("[uiHandler][handleMessage]Message=%s", msg));

                switch (msg.what){
                    case Config.ADD_ONE:
                        number++;
                        textView.setText(String.valueOf(number));
                        break;
                    default:
                        Log.d(TAG, String.format("[uiHandler][handleMessage]Other what of message %s", msg.what));
                        break;
                }
                super.handleMessage(msg);
            }
        };
    }

2. 创建普通线程，使用UI线程的Handler向UI线程发送数字增加消息。

public void startAddNumberThread(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(3000);
                    while (true) {
                        Message message = uiHandler.obtainMessage();
                        message.what = Config.ADD_ONE;
                        uiHandler.sendMessage(message);
                        Thread.sleep(1000);
                    }
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }).start();
    }

3. 实现效果。
   
4. 示例源码: handler进程通信-UpdateUIThread，有用的话敬请Star。

两个普通线程间的通信

1. 创建两个普通线程：threadA、threadB。
2. threadA创建后，等待1s（等threadB也完成创建），向threadB发送首条消息。
3. threadB收到threadA的消息后，回复1条消息。
4. threadA收到threadB回复的消息后，通信结束。
   

创建threadA，等待threadB创建完成后给threadB发送一条消息。

new Thread(new Runnable() {
    @Override
    public void run() {
        try {
            Looper.prepare();
            handlerA = new Handler() {
                @Override
                public void handleMessage(@NonNull Message msg) {
                    super.handleMessage(msg);
                    Log.d(TAG, String.format("[ThreadA][UseHandlerA][GetMessage]\t%s", msg.obj));
                }
            };
            // wait for handlerB isn't null
            Thread.sleep(1000);
            while (handlerB==null) {
                ;
            }
            Message msg = Message.obtain();
            msg.what = Config.THREADA;
            msg.obj = "Hi thread B, this's thread A";
            Log.d(TAG, String.format("[ThreadA][UseHandlerB][SendMessage]\t%s", msg.obj));
            handlerB.sendMessage(msg);
            //enter loop.
            Looper.loop();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}).start();

创建threadB。接收threadA发送的消息后回复一条消息。

new Thread(new Runnable() {
    @Override
    public void run() {
        Looper.prepare();
        handlerB = new Handler() {
            @Override
            public void handleMessage(@NonNull Message msg) {
                super.handleMessage(msg);
                Log.d(TAG, String.format("[ThreadB][UseHandlerB][GetMessage]\t%s", msg.obj));
                Message msgB = Message.obtain();
                msgB.what = Config.THREADA;
                switch (msg.what) {
                    case Config.THREADA:
                        msgB.obj = "Dear thread A, i'am fine, thanks and bye.";
                        Log.d(TAG, String.format("[ThreadB][UseHandlerA][SendMessage]\t%s", msgB.obj));
                        handlerA.sendMessage(msgB);
                        break;
                }
            }
        };
        Looper.loop();
    }
}).start();

结果输出

[ThreadA][UseHandlerB][SendMessage] Hi thread B, this's thread A
[ThreadB][UseHandlerB][GetMessage]  Hi thread B, this's thread A
[ThreadB][UseHandlerA][SendMessage] Dear thread A, i'am fine, thanks and bye.
[ThreadA][UseHandlerA][GetMessage]  Dear thread A, i'am fine, thanks and bye.

源码: handler进程通信-Demo2ThreadAToThreadB，有用的话敬请Star。

参考

【1】Android——Handler详解