Android example of using Thread and Handler

Android example of using Thread and Handler

This example show how to run code in background using Thread, and also show passing data from activity to thread by calling method of thread, and passing data from thread to activity with Handler.

MainActivity.java

package com.blogspot.android_er.androidthread;

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

 Button btnStart, btnStop, btnSend;
 EditText editTextMsgToSend;
 TextView textViewCntReceived, textViewMsgReceived;

 MyThread myThread;
 MyHandler myHandler;

 @Override
 protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 btnStart = (Button)findViewById(R.id.startthread);
 btnStop = (Button)findViewById(R.id.stopthread);
 btnSend = (Button)findViewById(R.id.send);
 editTextMsgToSend = (EditText)findViewById(R.id.msgtosend);
 textViewCntReceived = (TextView)findViewById(R.id.cntreceived);
 textViewMsgReceived = (TextView)findViewById(R.id.msgreceived);

 myHandler = new MyHandler(this);

 btnStart.setOnClickListener(btnStartOnClickListener);
 btnStop.setOnClickListener(btnStopOnClickListener);
 btnSend.setOnClickListener(btnSendOnClickListener);
 }

 View.OnClickListener btnStartOnClickListener =
 new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 if(myThread != null){
 myThread.setRunning(false);
 }
 myThread = new MyThread(myHandler);
 myThread.start();
 }
 };

 View.OnClickListener btnStopOnClickListener =
 new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 if(myThread != null){
 myThread.setRunning(false);
 myThread = null;
 }
 }
 };

 View.OnClickListener btnSendOnClickListener =
 new View.OnClickListener() {
 @Override
 public void onClick(View v) {
 if(myThread != null){
 myThread.msgToThread(editTextMsgToSend.getText().toString());
 }
 }
 };

 private void updateCnt(int cnt){
 textViewCntReceived.setText(String.valueOf(cnt));
 }

 private void updateMsg(String msg){
 textViewMsgReceived.setText(msg);
 }


 public static class MyHandler extends Handler{

 public static final int UPDATE_CNT = 0;
 public static final int UPDATE_MSG = 1;
 private MainActivity parent;

 public MyHandler(MainActivity parent) {
 super();
 this.parent = parent;
 }

 @Override
 public void handleMessage(Message msg) {

 switch (msg.what){
 case UPDATE_CNT:
 int c = (int)msg.obj;
 parent.updateCnt(c);
 break;
 case UPDATE_MSG:
 String m = (String)msg.obj;
 parent.updateMsg(m);
 break;
 default:
 super.handleMessage(msg);
 }

 }
 }
}

MyThread.java

package com.blogspot.android_er.androidthread;

import android.os.Looper;
import android.os.Message;

public class MyThread extends Thread{

 private int cnt;
 private boolean running;
 MainActivity.MyHandler mainHandler;

 public MyThread(MainActivity.MyHandler mainHandler) {
 super();
 this.mainHandler = mainHandler;
 }

 public void setRunning(boolean running){
 this.running = running;
 }

 public void msgToThread(String msgin){
 String msgout = new StringBuilder(msgin).reverse().toString();
 mainHandler.sendMessage(
 Message.obtain(mainHandler,
 MainActivity.MyHandler.UPDATE_MSG, msgout));
 }

 @Override
 public void run() {
 cnt = 0;
 running = true;

 String prompt;
 if(Looper.myLooper() == Looper.getMainLooper()){
 prompt = "myThread run in UI Thread";
 }else{
 prompt = "myThread run in NOT UI Thread";
 }
 mainHandler.sendMessage(
 Message.obtain(mainHandler,
 MainActivity.MyHandler.UPDATE_MSG, prompt));

 while (running){
 try {
 Thread.sleep(1000);
 mainHandler.sendMessage(
 Message.obtain(mainHandler,
 MainActivity.MyHandler.UPDATE_CNT, cnt));

 cnt++;
 } catch (InterruptedException e) {
 e.printStackTrace();
 }
 }
 }
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 
 
 android_layout_width="match_parent"
 android_layout_height="match_parent"
 android_padding="16dp"
 android_orientation="vertical"
 tools_context="com.blogspot.android_er.androidthread.MainActivity">

 <TextView
 android_layout_width="wrap_content"
 android_layout_height="wrap_content"
 android_layout_gravity="center_horizontal"
 android_autoLink="web"
 android_text="http://android-er.blogspot.com/"
 android_textStyle="bold" />

 <Button
 android_id="@+id/startthread"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_text="Start Thread"/>
 <Button
 android_id="@+id/stopthread"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_text="Stop Thread"/>
 <EditText
 android_id="@+id/msgtosend"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_hint="msg to send..." />
 <Button
 android_id="@+id/send"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_text="Send msg to thread"/>
 <TextView
 android_id="@+id/cntreceived"
 android_layout_width="match_parent"
 android_layout_height="wrap_content"
 android_textStyle="bold"
 android_textSize="26dp"/>
 <TextView
 android_id="@+id/msgreceived"
 android_layout_width="match_parent"
 android_layout_height="match_parent"
 android_textStyle="bold"
 android_textSize="20dp"/>
</LinearLayout>

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Related:
- Android example of using Service and BroadcastReceiver
- Example of IntentService and BroadcastReceiver

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