Data Structure
Networking
RDBMS
Operating System
Java
MS Excel
iOS
HTML
CSS
Android
Python
C Programming
C++
C#
MongoDB
MySQL
Javascript
PHP
Physics
Chemistry
Biology
Mathematics
English
Economics
Psychology
Social Studies
Fashion Studies
Legal Studies
- Selected Reading
- UPSC IAS Exams Notes
- Developer's Best Practices
- Questions and Answers
- Effective Resume Writing
- HR Interview Questions
- Computer Glossary
- Who is Who
How to cancel an executing AsyncTask in Android?
Before getting into example, we should know what is AsyncTask in android. AsyncTask going to do operations/actions in background thread and update on mainthread. While doing background operations on background thread, user can cancel operations by using the following code -
AsynTaskExample mAsyncTask = new AsyncTaskExample(); mAsyncTask.cancel(true);
This example demonstrate about how to cancel an executing AsyncTask in android.
Step 1 − Create a new project in Android Studio, go to File ⇒ New Project and fill all required details to create a new project.
Step 2 − Add the following code to res/layout/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:id = "@+id/rootview" android:layout_width = "match_parent" android:layout_height = "match_parent" android:orientation = "vertical" android:background = "#c1c1c1" android:gravity = "center_horizontal" tools:context = ".MainActivity"> <Button android:id = "@+id/asyncTask" android:text = "Download" android:layout_width = "wrap_content" android:layout_height = "wrap_content" /> <ImageView android:id = "@+id/image" android:layout_width = "300dp" android:layout_height = "300dp" /> </LinearLayout>
In the above code when you click on button it going to download image from internet source and append to imageview.
Step 3 − Add the following code to src/MainActivity.java
package com.example.andy.myapplication;
import android.app.ProgressDialog;
import android.content.DialogInterface;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
public class MainActivity extends AppCompatActivity {
URL ImageUrl = null;
InputStream is = null;
Bitmap bmImg = null;
ImageView imageView = null;
AsyncTaskExample asyncTask = null;
ProgressDialog p;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Button button = findViewById(R.id.asyncTask);
imageView = findViewById(R.id.image);
button.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
asyncTask = new AsyncTaskExample();
asyncTask.execute("https://www.tutorialspoint.com/images/tp-logo-diamond.png");
}
});
}
private class AsyncTaskExample extends AsyncTask {
@Override
protected void onPreExecute() {
super.onPreExecute();
p = new ProgressDialog(MainActivity.this);
p.setMessage("Please wait...It is downloading");
p.setIndeterminate(true);
p.setCancelable(true);
p.setOnCancelListener(new DialogInterface.OnCancelListener() {
@Override
public void onCancel(DialogInterface dialog) {
asyncTask.cancel(true);
Toast.makeText(MainActivity.this,"AsyncTask is stopped",Toast.LENGTH_LONG).show();
}
});
p.show();
}
@Override
protected Bitmap doInBackground(String... strings) {
try {
try {
Thread.sleep(10000);
} catch (InterruptedException e) {
e.printStackTrace();
}
ImageUrl = new URL(strings[0]);
HttpURLConnection conn = (HttpURLConnection) ImageUrl .openConnection();
conn.setDoInput(true);
conn.connect();
is = conn.getInputStream();
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.RGB_565;
bmImg = BitmapFactory.decodeStream(is, null, options);
} catch (IOException e) {
e.printStackTrace();
}
return bmImg;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
if(imageView! = null) {
p.hide();
imageView.setImageBitmap(bitmap);
} else {
p.show();
}
}
}
}Step 4− Add the following code to manifest.xml
<?xml version = "1.0" encoding = "utf-8"?> <manifest xmlns:android = "http://schemas.android.com/apk/res/android" package = "com.example.andy.myapplication"> <uses-permission android:name = "android.permission.INTERNET"/> <application android:allowBackup = "true" android:icon = "@mipmap/ic_launcher" android:label = "@string/app_name" android:roundIcon = "@mipmap/ic_launcher_round" android:supportsRtl = "true" android:theme = "@style/AppTheme"> <activity android:name = ".MainActivity"> <intent-filter> <action android:name = "android.intent.action.MAIN" /> <category android:name = "android.intent.category.LAUNCHER" /> </intent-filter> </activity> </application> </manifest>
In the above code we have given internet permission to fetch an image from internet source.
Let's try to run your application. I assume you have connected your actual Android Mobile device with your computer. To run the app from android studio, open one of your project's activity files and click Run 
Icon from the toolbar. Select your mobile device as an option and then check your mobile device which will display your default screen −
When you click on the above button, it will start a progressbar, click on any place rather than progressbar it will show the following screen.
The above screen clearly shows the async task is stopped and image is now downloaded from internet source.
If you dont stop async task it will download an image as shown above
Click here to download the project code
1K+ Views
