MediaPlayer doesn't start with method call from other class

Question

I have a weird problem with this code whilst the error is simple I don't understand it.

Class with MediaPlayer sound and methods:

public class Sounds {

private MediaPlayer stone;
private MediaPlayer gong;

public Sounds(Context con, int stoneSound, int gongSound){
    this.stone = MediaPlayer.create(con, stoneSound);
    this.gong  = MediaPlayer.create(con, gongSound);
}

public void ActivateStone(){
    MediaPlayer auxStone = this.stone;
    auxStone.start(); //THIS IS THE LINE 19 of "Sounds.java:19" log error
    auxStone.setOnCompletionListener(new OnCompletionListener() {
        @Override
        public void onCompletion(MediaPlayer mp) {
            mp.release();
        }
    });
}

public void ActivateGong(){
    MediaPlayer auxGong = this.gong;
    auxGong.start();
    auxGong.setOnCompletionListener(new OnCompletionListener() {
        @Override
        public void onCompletion(MediaPlayer mp) {
            mp.release();
        }
    });
}

Now the thread that calls the method to use the "sound" each interval

public void run() {
    while (!stoped) {
        try {
            this.sleep(interval);
            if (stones == mode || stones == (mode * 2)) {
                sounds.ActivateGong();
            } else {
                sounds.ActivateStone(); //THIS IS THE LINE 32 in "Counter.java:32" log error
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        stones += 1;
        handler.setHcron(stones + "");
        handler.act();
    }
}

The sounds ONLY play once and then the app throws an exception with this log:

05-09 19:10:52.306: E/AndroidRuntime(479): FATAL EXCEPTION: Thread-9448
05-09 19:10:52.306: E/AndroidRuntime(479): Process: contador.piedras.jugger, PID: 479
05-09 19:10:52.306: E/AndroidRuntime(479): java.lang.IllegalStateException
05-09 19:10:52.306: E/AndroidRuntime(479):  at android.media.MediaPlayer._start(Native Method)
05-09 19:10:52.306: E/AndroidRuntime(479):  at android.media.MediaPlayer.start(MediaPlayer.java:1074)
05-09 19:10:52.306: E/AndroidRuntime(479):  at contador.piedras.jugger.Sounds.ActivateStone(Sounds.java:19)
05-09 19:10:52.306: E/AndroidRuntime(479):  at contador.piedras.jugger.Counter.run(Counter.java:32)

Answer 1

Maybe you should try to add sync, it can be cause of threads :

    synchronized (auxStone) {
         auxStone.start(); //THIS IS THE LINE 19 of "Sounds.java:19" log error
        auxStone.setOnCompletionListener(new OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                mp.release();
            }
        });
    }

EDIT: as documentation declares, this method : Throws: IllegalStateException - if it is called in an invalid state. So you need to check it for playing by if(!auxStone.isPlaying())