AsyncTask: perform background operations and publish results on the UI thread

This exercise have the same effect of "Android background thread, by extending Thread" and "Android background thread, by implementing Thread object, provided with a Runnable object". It is implemented in AsyncTask instead of Thread.



AsyncTask enables proper and easy use of the UI thread. This class allows to perform background operations and publish results on the UI thread without having to manipulate threads and/or handlers.

An asynchronous task is defined by a computation that runs on a background thread and whose result is published on the UI thread. An asynchronous task is defined by 3 generic types, called Params, Progress and Result, and 4 steps, called begin, doInBackground, processProgress and end.

main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
  android:orientation="vertical"
  android:layout_width="fill_parent"
  android:layout_height="fill_parent"
  >
<TextView
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:text="@string/hello"
  />
<TextView
  android:id="@+id/mytext"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:text="This Text will be Turn ON/OFF triggered by AsyncTask."
  />
</LinearLayout>

AndroidBackgroundAsyncTask.java

package com.exercise.AndroidBackgroundAsyncTask;

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

public class AndroidBackgroundAsyncTask extends Activity {

TextView myText;

  public class BackgroundAsyncTask extends
  AsyncTask<Void, Boolean, Void> {
  
   boolean myTextOn;

 @Override
 protected Void doInBackground(Void... params) {
  // TODO Auto-generated method stub
 
  while(true)
  {
   myTextOn = !myTextOn;
   publishProgress(myTextOn);
   SystemClock.sleep(1000);
  }
  //return null;
 }

 @Override
 protected void onPostExecute(Void result) {
  // TODO Auto-generated method stub
  //it will never been shown in this exercise...
  Toast.makeText(AndroidBackgroundAsyncTask.this,
    "onPostExecute", Toast.LENGTH_LONG).show();
 }

 @Override
 protected void onPreExecute() {
  // TODO Auto-generated method stub
  myTextOn = true;
  Toast.makeText(AndroidBackgroundAsyncTask.this,
    "onPreExecute", Toast.LENGTH_LONG).show();
 }

 @Override
 protected void onProgressUpdate(Boolean... values) {
  // TODO Auto-generated method stub

  if (values[0]){
   myText.setVisibility(View.GONE);
  }
  else{
   myText.setVisibility(View.VISIBLE);
  }
 }


}

/** Called when the activity is first created. */
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      myText = (TextView)findViewById(R.id.mytext);
    
      new BackgroundAsyncTask().execute();
  }
}

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Related Article: onPostExecute() of AsyncTask

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