Question

I’ve written a AsyncTask:

public class AudioTransition extends AsyncTask <Void, Void, MediaPlayer>
{   
    private int goalID;
    private int milliseconds;
    private MediaPlayer tempPlayer;

    AudioTransition(int ID, int Milliseconds)
    {
        goalID = ID;
        milliseconds = (int)(((float)Milliseconds)/100);
    }

    @Override
    protected void onPreExecute()
    {
       tempPlayer = MediaPlayer.create(context, goalID);
       tempPlayer.setVolume(0, 0);
       tempPlayer.setLooping(true);
       tempPlayer.start();
    }

    @Override
    protected MediaPlayer doInBackground(Void... arg0) {

        for (int i = 0; i < 100; i++)
        {
            value = i;

            publishProgress();
            try {
                Thread.sleep(milliseconds);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            if (!player.isPlaying())
                tempPlayer.pause();
        }

        return tempPlayer;
    }

    @Override
    protected void onProgressUpdate(Void... v) {
        super.onProgressUpdate(v);
        player.setVolume(100-value, 100-value);
        tempPlayer.setVolume(value, value);
    }


    @Override
    protected void onPostExecute( MediaPlayer result )  {
          super.onPostExecute(result);
          player.reset();
          player = tempPlayer;
          player.setVolume(100,100);
          transitioning = false;
    }
}

But the volume doesn’t fade out. It just starts both tracks, then stops. The MediaPlayers are not updated until doInBackground completes. How can I make the MediaPlayers get updated within this type of background worker? It seems like the publishProgress() thing should work.

Answer 1

Oh lord. Dont be sleeping threads inside of AsyncTask! You are completely misusing AsyncTask. You couldn’t think of another way to do a timer type thing, so you’re latching onto the idea of publishprogress from AsyncTask (which doesn’t even work how I think you think it works) even though AsyncTask should be used for one thing and one thing only: doing heavy work off of the main (UI) thread.

If you just wanted to fade the volume out then use something like this: (this goes somewhere outside of any method).

 private Runnable VolumeFadeRunnable = new Runnable() {
        @Override
        public void run() {
                volume--;
             player.setVolume(volume, volume);
                 if(volume>0)
               handler.postDelayed(this, 1000);
                 else
                   handler.removeCallbacks(this);
        }
    };

just initialize your handler as a field inside of onCreate or whatever and make sure that and the counter variable are visible inside of that runnable.