Android SDK AsyncTask doInBackground not running (subclass)

Question

As of 15/2/2012 I have yet to find a good explanation to nor a reason why this does not work. The closest to a solution is to use the traditional Thread approach, but then why include a class that does not (seem to) work in the Android SDK?

Evenin' SO!

I have an AsyncTask subclass:

// ParseListener had a callback which was called when an item was parsed in a
// RSS-xml, but as stated further down it is not used at all right now.
private class xmlAsync extends AsyncTask<String, RSSItem, Void> implements ParseListener

That is executed like this:

xmlAsync xmlThread = new xmlAsync();

xmlThread.execute("http://www.nothing.com");

Now this subclass has run into a little error. Previously it did some xml-parsing, but when I noticed that it's doInBackground() wasn't called I stripped it down, line by line, finally ending up with just this:

@Override
protected Void doInBackground(String... params) 
{
    Log.v(TAG, "doInBackground");
        return null;
}

Which, for some reason, logged nothing. However, I added this:

@Override
protected void onPreExecute() 
{
        Log.v(TAG, "onPreExecute");
        super.onPreExecute();
}

And that line is indeed logged when executing the thread. So somehow onPreExecute() is called but not doInBackground(). I have another AsyncTask running in the background at the same time which works just fine.

I'm currently running the app on an emulator, SDK Version 15, Eclipse, Mac OS X 10.7.2, close to the North Pole.

EDIT:

@Override
    protected void onProgressUpdate(RSSItem... values) {

        if(values[0] == null)
        {
                            // activity function which merely creates a dialog
            showInputError();
        }
        else
        {

            Log.v(TAG, "adding "+values[0].toString());
            _tableManager.addRSSItem(values[0]);
        }


        super.onProgressUpdate(values);
    }

_tableManager.addRSSItem() more or less adds a row to a SQLiteDatabase, initialized with the activity's context. publishProgress() is called by the Interface ParseListener's callback. However, since I don't even do anything except log.v in doInBackground() I first found this unnecessary to even bring up.

EDIT 2:

Alright, just to be perfectly clear, this is the other AsyncTask, executing in the same activity and working perfectly fine.

private class dbAsync extends AsyncTask<Void, RSSItem, Void>
{
    Integer prevCount;
    boolean run;

    @Override
    protected void onPreExecute() {
        run = true;
        super.onPreExecute();
    }

    @Override
    protected Void doInBackground(Void... params) {
        // TODO Auto-generated method stub
        run = true;
        prevCount = 0;

        while(run)
        {
            ArrayList<RSSItem> items = _tableManager.getAllItems();

            if(items != null)
            {
                if(items.size() > prevCount)
                {
                    Log.v("db Thread", "Found new item(s)!");
                    prevCount = items.size();

                    RSSItem[] itemsArray = new RSSItem[items.size()];

                    publishProgress(items.toArray(itemsArray));
                }
            }               

            SystemClock.sleep(5000);
        }

        return null;
    }

    @Override
    protected void onProgressUpdate(RSSItem... values) {

        ArrayList<RSSItem> list = new ArrayList<RSSItem>();

        for(int i = 0; i < values.length; i++)
        {
            list.add(i, values[i]);
        }

        setItemsAndUpdateList(list);

        super.onProgressUpdate(values);
    }

    @Override
    protected void onCancelled() {
        run = false;

        super.onCancelled();
    }
}

EDIT 3:

Sigh, sorry I'm bad at asking questions. But here is the initialization of the Tasks.

xmlAsync _xmlParseThread;
dbAsync _dbLookup;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

_dbLookup = new dbAsync();
_dbLookup.execute();

_xmlParseThread = new xmlAsync();       
_xmlParseThread.execute("http://www.nothing.com", null);
}

Answer 1

You should checkout this answer: https://stackoverflow.com/a/10406894/347565 and the link to google groups it includes.

I had a similar problem as you, still unclear why it is not working, but I changed my code like this and problem is gone:

ASyncTask<Void,Void,Void> my_task = new ASyncTask<Void,Void,Void>() { ... };
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB)
    my_task.executeOnExecutor(AsyncTask.THREAD_POOL_EXECUTOR, (Void[])null);
else
    my_task.execute((Void[])null);