AsyncTask onPostExecute never gets called

Question

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.

Answer 1

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.

Answer 2

There's one more gotcha about AsyncTasks that I just spent half the day on:

The AsyncTask class must be loaded on the UI thread. This is done automatically as of JELLY_BEAN.

Says the documentation. On Gingerbread (and probably before), given the right circumstances, this leads to onPostExecute not being run. The solution, however, is easy, just a

new MyAsyncTask(); 

early in the UI thread so the class gets loaded before anything in the background can inadvertently load it.

I had used a static function in my AsyncTask subclass from a background thread that, depending on timing, got called before anything on the UI thread used that AsyncTask subclass, and bingo, a nice Heisenbug.

(Bear with me for answering this old, already answered question, but I didn't find that tidbit of info anywhere, and this is my first post)