Android AsyncTask

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

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. 

the source code is given below, please have a look. make a project AsyncTask and have a MainActivity with name MainActivity.java, the code is given below.

MainACtivity.java

package com.jitesh.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 MainActivity extends Activity {

 

Button btn_start;

ProgressBar progressBar;

TextView txt_percentage;

   @Override

   public void onCreate(Bundle savedInstanceState) {

       super.onCreate(savedInstanceState);

       setContentView(R.layout.activity_main);

        

       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(MainActivity.this,

           "Invoke onPreExecute()", Toast.LENGTH_SHORT).show();

 

   progress_status = 0;

   txt_percentage.setText("downloading 0%");

   

 }

     

 @Override

 protected Void doInBackground(Void... params) {

   //write the code which you do in background like downloading or using so internet resources etc

  while(progress_status<100){

    

   progress_status += 10;

    

   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(MainActivity.this,

           "Invoke onPostExecute()", Toast.LENGTH_SHORT).show();

    

   txt_percentage.setText("download complete");

   btn_start.setEnabled(true);

 }

   }

}

/res/layout/activity_main.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>

res/values/strings

<?xml version="1.0" encoding="utf-8"?>

<resources>

    <string name="app_name">AsyncTask</string>

    <string name="hello_world">Hello world!</string>

    <string name="menu_settings">Settings</string>

     <string name="start_btn">Start Button</string>

    <string name="async_task">Async Task</string>

</resources>

res/values/dimens

<resources>

    <dimen name="padding_small">8dp</dimen>

    <dimen name="padding_medium">8dp</dimen>

    <dimen name="padding_large">16dp</dimen>

</resources>