onPostExecute() of AsyncTask

In my old exercise "AsyncTask: perform background operations and publish results on the UI thread", doInBackground() is a infinite loop without return, such that the onPostExecute() method will not be called.

In order to make onPostExecute() taking effect, a button to stop the background task is implemented. When user click on the button, the onPostExecute() will end with and return, and onPostExecute() will be called.



Modify main.xml to add a Stop button.

<?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"
  />
<Button
  android:id="@+id/stop"
  android:layout_width="fill_parent"
  android:layout_height="wrap_content"
  android:text="Stop"
  />
<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>

Modify 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.Button;
import android.widget.TextView;
import android.widget.Toast;

public class AndroidBackgroundAsyncTask extends Activity {

TextView myText;
boolean stopRun = false;

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

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

 @Override
 protected void onPostExecute(Void result) {
  // TODO Auto-generated method stub
  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);
    
      Button buttonStop =  (Button)findViewById(R.id.stop);
      buttonStop.setOnClickListener(new Button.OnClickListener(){

  @Override
  public void onClick(View v) {
   // TODO Auto-generated method stub
   stopRun = true;
  }});
    
      new BackgroundAsyncTask().execute();
  }
}

Download the files.

Related article:
- ProgressBar running in AsyncTask