Android example of using Thread and Handler

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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 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: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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