Android Handler: The child thread sends a message to the UI main thread

Activity code:

public class MainActivity extends Activity {
    private MyThread myThread;
    private Handler handler; //The child thread communicates with the UI main thread

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate (savedInstanceState);
        setContentView(R.layout.main);

        //Get the message pushed by the child thread through the Handler
		handler = new Handler () {
			@Override
			public void handleMessage(Message msg) {
				super.handleMessage(msg);
				Bundle bundle = msg.getData();
				String value = bundle.getString("value");
				outputEditText.setText(value);
			}
		};

		// start a child thread
		myThread = new MyThread(handler);
		myThread.start();

		showDialog("Socket Thread Started!");
    }

    /**
     * Dialog display
     */
    private void showDialog(String msg){
        new AlertDialog.Builder(this)
                .setTitle("Title")
                .setMessage(msg)
                .setPositiveButton("ok", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {

            }
        }).show();
    }
}

 

Thread code:

public class MyThread extends Thread{
    private Handler handler;

    public MyThread(Handler handler){
        this.handler = handler;
    }

    @Override
    public void run() {
        try {
            //Continuously send the current date and time to the UI main thread
            while(true){
                TimeUnit.MILLISECONDS.sleep(1000);

                SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
                String date = sdf.format(new Date());

                sendMessage(date);
            }
        } catch (Exception e) {
            e.printStackTrace ();
        }
    }

    /**
     * Send a message to the UI main thread
     */
    private void sendMessage(String msg){
        Bundle data = new Bundle();
        data.putString("value", msg);

        Message message = new Message();
        message.setData(data);

        this.handler.sendMessage(message);
    }
}

 

Handle instantiation when UI needs to be refreshed:

        In the main thread: Handler handler = new Handler();

        In other thread: Handler handler = new Handler(Looper.getMainLooper());

 

Handle instantiation without refreshing the UI:

        In the main thread: Handler handler = new Handler();

        In other threads: 

                Looper.prepare(); 

                Handler handler = new Handler ();

                Looper.loop();

 

                or

 

                Handler handler = new Handler(Looper.getMainLooper());

 

        message.what is generally used to distinguish messages. SetData(Bundle) can be used to transfer data within the process, and message.obj can be used to transfer serializable object data between processes