Android – AsyncTask onPostExecute never gets called

androidandroid-asynctask

I am not sure what I am doing wrong but onPostExecute never gets called.

Created a base class called BaseActivity.java
From my original Activity I extended this class.
Placed PostToOpenFeint class inside BaseActivity
Called it from the UI thread from the main activity my doing:
```
new PostToOpenFeint.execute();
```

The onPreExecute(), doInBackground(..) gets triggered, but for some reason the onPostExecute never gets called.

Thank you in Advance!

Dave

 private class PostToOpenFeint extends AsyncTask<Void, Void, Void> {
  /*
   * (non-Javadoc)
   * 
   * @see android.os.AsyncTask#doInBackground(Params[])
   */
  @Override
  protected Void doInBackground(Void... params) {
   // does all the work here
   return null;
  }


  /*
   * (non-Javadoc)
   * 
   * @see android.os.AsyncTask#onPostExecute(java.lang.Object)
   */
  @Override
  protected void onPostExecute(Void result) {
   // TODO Auto-generated method stub
   super.onPostExecute(result);
   Toast.makeText(MainScreen.this, "Done syncing", Toast.LENGTH_LONG).show();
  }

  /*
   * (non-Javadoc)
   * 
   * @see android.os.AsyncTask#onPreExecute()
   */
  @Override
  protected void onPreExecute() {
   // TODO Auto-generated method stub
   super.onPreExecute();
   Toast.makeText(MainScreen.this, "About to sync all your scores", Toast.LENGTH_LONG).show();
  }

Looking into it more, this is what I was able to observe. For example if I place this call:

 new PostToOpenFeint.execute();

right after onCreate of the Activity, then everything works fine. If I place this call say inside a button listener.

settingsButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
   new PostToOpenFeint.execute();
}
});

The onPostExecute() never gets called, not sure what I am doing wrong. The restriction I read was to call this from UI Thread and I am calling it from UI thread.

Best Answer

I had a similiar problem just now. I was extending AsyncTask<Integer,Integer,Integer> and my onPostExecute method looked like:

protected void onPostExecute(int result)

This seemed OK to me, but then again I'm more of a .NET guy than a Java guy. I changed it to:

protected void onPostExecute(Integer result)

because for some reason Java thinks there is a difference between int and Integer?

I think that your problem is that you're declaring the return type as void in your:

extends<Void,Void,Void>

That means no params, no progress and no result. If you want to execute something when it's done, I think you need to give it some kind of value like and integer or a boolean.

If you change your extends to:

<Void,Void,Integer>

Now your passing no params, not publishing any progress, but are returning a value. Change your onPostExecute method to accept an Integer:

protected void onPostExecute(Integer result)

Then change the return in your doInBackground method to something like:

return 1;

Then it should execute for you.

Related Solutions

Android – AsyncTask Android example

My full answer is here, but here is an explanatory image to supplement the other answers on this page. For me, understanding where all the variables were going was the most confusing part in the beginning.

Android – How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class

Easy:

Create interface class, where String output is optional, or can be whatever variables you want to return.
```
 public interface AsyncResponse {
     void processFinish(String output);
 }
```

Go to your AsyncTask class, and declare interface AsyncResponse as a field :

 public class MyAsyncTask extends AsyncTask<Void, Void, String> {
   public AsyncResponse delegate = null;

     @Override
     protected void onPostExecute(String result) {
       delegate.processFinish(result);
     }
  }

In your main Activity you need to implements interface AsyncResponse.

 public class MainActivity implements AsyncResponse{
   MyAsyncTask asyncTask =new MyAsyncTask();

   @Override
   public void onCreate(Bundle savedInstanceState) {

      //this to set delegate/listener back to this class
      asyncTask.delegate = this;

      //execute the async task 
      asyncTask.execute();
   }

   //this override the implemented method from asyncTask
   @Override
   void processFinish(String output){
      //Here you will receive the result fired from async class 
      //of onPostExecute(result) method.
    }
  }

UPDATE

I didn't know this is such a favourite to many of you. So here's the simple and convenience way to use interface.

still using same interface. FYI, you may combine this into AsyncTask class.

in AsyncTask class :

public class MyAsyncTask extends AsyncTask<Void, Void, String> {

  // you may separate this or combined to caller class.
  public interface AsyncResponse {
        void processFinish(String output);
  }

  public AsyncResponse delegate = null;

    public MyAsyncTask(AsyncResponse delegate){
        this.delegate = delegate;
    }

    @Override
    protected void onPostExecute(String result) {
      delegate.processFinish(result);
    }
}

do this in your Activity class

public class MainActivity extends Activity {
  
   MyAsyncTask asyncTask = new MyAsyncTask(new AsyncResponse(){
    
     @Override
     void processFinish(String output){
     //Here you will receive the result fired from async class 
     //of onPostExecute(result) method.
     }
  }).execute();

 }

Or, implementing the interface on the Activity again

public class MainActivity extends Activity 
    implements AsyncResponse{
      
    @Override
    public void onCreate(Bundle savedInstanceState) {

        //execute the async task 
        new MyAsyncTask(this).execute();
    }
      
    //this override the implemented method from AsyncResponse
    @Override
    void processFinish(String output){
        //Here you will receive the result fired from async class 
        //of onPostExecute(result) method.
    }
}

As you can see 2 solutions above, the first and third one, it needs to create method processFinish, the other one, the method is inside the caller parameter. The third is more neat because there is no nested anonymous class.

Tip: Change String output, String response, and String result to different matching types in order to get different objects.

Best Answer

Related Solutions

Android – AsyncTask Android example

Android – How to get the result of OnPostExecute() to main activity because AsyncTask is a separate class

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