Handler asynchronous message processing mechanism

Asynchronous Message processing in Android mainly consists of four parts: Message, Handler, MessageQueue and Looper.

Message: responsible for inter thread message delivery

Handler: used to send and receive information

MessageQueue: the queue used to store messages. Each thread has only one such object

Looper: used to continuously monitor the existence of messages in the queue and take them out

Direct instance code

Display an increasing number every second

public class MainActivity extends AppCompatActivity {
    private static final int UPDATE=0x1;
    private int flag = 0;
    private TextView text;
    private Handler handler=new Handler() {
        @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                case UPDATE:
                    text.setText(String.valueOf(msg.arg1));
                    break;
            }
        }
    };
    private Runnable thread=() -> {
        while (true) {
            try {
                Thread.sleep(1000);
                Message msg = new Message();
                msg.what = UPDATE;
                msg.arg1 = flag++;
                handler.sendMessage(msg);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        text = (TextView)findViewById(R.id.text);
        Thread thread1 = new Thread(thread);
        thread1.start();
    }
}

The same function can be achieved by using the timer provided by the Handler

public class MainActivity extends AppCompatActivity {
    private static final int UPDATE=0x1;
    private int flag = 0;
    private TextView text;
    private Handler handler = new Handler();
    private Runnable thread= new Runnable() {
        public void run() {
            handler.postDelayed(this, 1000);
            text.setText(String.valueOf(flag++));
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);
        text = (TextView)findViewById(R.id.text);
        handler.post(thread);
    }
}