AsyncTask Android example | AsyncTask in Android

In this tutorial you will learn how to use AsyncTask in your application. This AsyncTask class perform background operations and update the results on the UI

AsyncTask has three generic type

• Params, the type of the parameters sent to the task upon execution.
• Progress, the type of the progress units published during the background computation.
• Result, the type of the result of the background computation

Private class ShowDialogAsyncTask extends 
        AsyncTask<Params, Progress, Result>{....}

AsyncTask goes through 4 steps

• onPreExecute(),invoked on the UI thread immediately after the task is executed.
•  doInBackground(Paaram ...),invoked on the background thread immediately after onPreExecute() finishes executing.
• onProgressUpdate(Progress...) invoked on the UI thread after a call to publishProgress(Progress...).
•  onPostExecute(Result), invoked on the UI thread after the background computation finishes. 

AsyncTaskActivity

package com.javasrilankansupport.asynctask;

import android.os.AsyncTask;
import android.os.Bundle;
import android.os.SystemClock;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.ProgressBar;
import android.widget.TextView;
import android.widget.Toast;


public class AsyncTaskActivity extends Activity {

 Button btn_start;
 ProgressBar progressBar;
 TextView txt_percentage;
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_async_task);
        
        btn_start = (Button) findViewById(R.id.btn_start);
        progressBar =  (ProgressBar) findViewById(R.id.progress);
        txt_percentage= (TextView) findViewById(R.id.txt_percentage);
        
        btn_start.setOnClickListener(new View.OnClickListener() {
   
   @Override
   public void onClick(View v) {
    
    btn_start.setEnabled(false);
    new ShowDialogAsyncTask().execute();
   }
  });
    }

    
    private class ShowDialogAsyncTask extends AsyncTask<Void, Integer, Void>{

     int progress_status;
     
     @Override
  protected void onPreExecute() {
   // update the UI immediately after the task is executed
   super.onPreExecute();
   
    Toast.makeText(AsyncTaskActivity.this,
            "Invoke onPreExecute()", Toast.LENGTH_SHORT).show();

    progress_status = 0;
    txt_percentage.setText("downloading 0%");
   
  }
     
  @Override
  protected Void doInBackground(Void... params) {
   
   while(progress_status<100){
    
    progress_status += 2;
    
    publishProgress(progress_status);
    SystemClock.sleep(300);
    
   }
   return null;
  }
 
  @Override
  protected void onProgressUpdate(Integer... values) {
   super.onProgressUpdate(values);
   
   progressBar.setProgress(values[0]);
   txt_percentage.setText("downloading " +values[0]+"%");
   
  }
  
  @Override
  protected void onPostExecute(Void result) {
   super.onPostExecute(result);
   
    Toast.makeText(AsyncTaskActivity.this,
            "Invoke onPostExecute()", Toast.LENGTH_SHORT).show();
    
    txt_percentage.setText("download complete");
    btn_start.setEnabled(true);
  }
    }
}

activity_async_task.xml

<RelativeLayout 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" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:padding="@dimen/padding_medium"
        android:text="@string/async_task"
        tools:context=".AsyncTaskActivity" />

    <ProgressBar
        android:id="@+id/progress"
        style="?android:attr/progressBarStyleHorizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_marginTop="34dp" />

    <Button
        android:id="@+id/btn_start"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/progress"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="40dp"
        android:minWidth="120dp"
        android:text="@string/start_btn" />

    <TextView
        android:id="@+id/txt_percentage"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentLeft="true"
        android:layout_below="@+id/progress"
        android:text="downloading  0%"
        android:textAppearance="?android:attr/textAppearanceMedium" />

</RelativeLayout>

Download AsyncTask Android example

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