HandlerThread

[embedyt]https://www.youtube.com/watch?v=n0mkYSjldeA[/embedyt]

In this tutorial, we will learn how to use the HandlerThread class on Android, which is a subclass of the normal Java Thread that initiates a MessageQueue and a Looper in it’s run method. This way, it keeps running until we call quit on it and accepts new work packages in form of Messages and Runnables.
To get work into a HandlerThread, we need a Handler, which we can initialize either in the onLooperPrepared callback in a HandlerThread subclass, or by passing the HandlerThread’s Looper explicitly with getLooper.
The Handler has different methods available to send and create Messages and Runnables, like post, postDelayed, postAtTime, postAtFrontOfQueue, send, sendDelayed, sendAtTime, sendAtFrontOfQueue, sendEmptyMessage, sendEmptyMessageDelayed, sendEmptyMessageAtTime and different obtain variations that take different combinations of arguments. With setTarget, we can specify the Handler that a Message should be dispatched to, and with sendToTarget send it to the corresponding MessageQueue.
Messages can hold data in their what, arg1, arg2, and obj fields, and we can attach an additional data Bundle with setData. To read this data, we have to override the Handler’s handleMessage method.
When we instantiate a HandlerThread, we should specify a thread priority with the Process.THREAD_PRIORITY constants, either over the constructor or by calling Process.setThreadPriority.
With quit and quitSafely we can leave the MessageQueue of a HandlerThread. But we can also remove Messages and Runnables from its MessageQueue without quitting the Looper, by calling removeMessages, removeCallbacks or removeCallbacksAndMessages, which can also take an object token argument to identify the Message more specifically.

Watch this playlist to learn more about the underlying concepts (Thread, MessageQueue, Looper, etc.):
youtube.com/playlist?list=PLrnPJCHvNZuDl4WUKi26WbzLMsM1sXCD4

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activity_main.xmlMainActivity.javaExampleHandlerThread.java
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    tools:context="com.codinginflow.handlerthreadexample.MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="doWork"
        android:text="Do work" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:onClick="removeMessages"
        android:text="Remove messages" />

</LinearLayout>
package com.codinginflow.handlerthreadexample;

import android.os.Bundle;
import android.os.Message;
import android.os.SystemClock;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.view.View;

import static com.codinginflow.handlerthreadexample.ExampleHandlerThread.EXAMPLE_TASK;

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";

    private ExampleHandlerThread handlerThread = new ExampleHandlerThread();

    private ExampleRunnable1 runnable1 = new ExampleRunnable1();
    private Object token = new Object();

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

        handlerThread.start();
    }

    public void doWork(View view) {
        Message msg = Message.obtain(handlerThread.getHandler());
        msg.what = EXAMPLE_TASK;
        msg.arg1 = 23;
        msg.obj = "Obj String";
        //msg.setData();

        msg.sendToTarget();
        //handlerThread.getHandler().sendEmptyMessage(1);

        handlerThread.getHandler().postAtTime(runnable1, token, SystemClock.uptimeMillis());
        handlerThread.getHandler().post(runnable1);
        //handlerThread.getHandler().post(new ExampleRunnable1());
        //handlerThread.getHandler().postAtFrontOfQueue(new ExampleRunnable2());
    }

    public void removeMessages(View view) {
        handlerThread.getHandler().removeCallbacks(runnable1, token);
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        handlerThread.quit();
    }

    static class ExampleRunnable1 implements Runnable {
        @Override
        public void run() {
            for (int i = 0; i < 4; i++) {
                Log.d(TAG, "Runnable1: " + i);
                SystemClock.sleep(1000);
            }
        }
    }

    static class ExampleRunnable2 implements Runnable {
        @Override
        public void run() {
            for (int i = 0; i < 4; i++) {
                Log.d(TAG, "Runnable2: " + i);
                SystemClock.sleep(1000);
            }
        }
    }
}

package com.codinginflow.handlerthreadexample;

import android.annotation.SuppressLint;
import android.os.Handler;
import android.os.HandlerThread;
import android.os.Message;
import android.os.Process;
import android.os.SystemClock;
import android.util.Log;

public class ExampleHandlerThread extends HandlerThread {
    private static final String TAG = "ExampleHandlerThread";

    public static final int EXAMPLE_TASK = 1;

    private Handler handler;

    public ExampleHandlerThread() {
        super("ExampleHandlerThread", Process.THREAD_PRIORITY_BACKGROUND);
    }

    @SuppressLint("HandlerLeak")
    @Override
    protected void onLooperPrepared() {
        handler = new Handler() {
            @Override
            public void handleMessage(Message msg) {
                switch (msg.what) {
                    case EXAMPLE_TASK:
                        Log.d(TAG, "Example Task, arg1: " + msg.arg1 + ", obj: " + msg.obj);
                        for (int i = 0; i < 4; i++) {
                            Log.d(TAG, "handleMessage: " + i);
                            SystemClock.sleep(1000);
                        }
                        break;
                }
            }
        };
    }

    public Handler getHandler() {
        return handler;
    }
}