Android one MediaPlayer instance - singleton

Question

I am about to create simple android app to play sound on a button click but I struggle with understanding singleton design pattern which would be very helpful in this application. What I try to achieve is to have number of activities and share only one MediaPlayer instance among them so that wehen user presses the button sound plays and if he will press the same or another button on same or different activity the sound will stop.

Here is my code but after pressing the button twice another instance of MediaPlayer is created and you can here the same sound being played at the same time

public class MyMediaPlayer {
MediaPlayer mp;
private static volatile MyMediaPlayer instance = null;
private MyMediaPlayer() { }

public static MyMediaPlayer getInstance() {
    if (instance == null) {
        synchronized (MyMediaPlayer.class) {
            if (instance == null) {
                instance = new MyMediaPlayer();
            }
        }
    }

    return instance;
}
}

and MainActivity.java:

public class MainActivity extends Activity {

private MyMediaPlayer player = getInstance();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

}

public void playSound(View view){
    player.mp = MediaPlayer.create(getApplicationContext(), R.raw.sound);
    player.mp.start();
}
}

As I am not very experienced could you in addition to tips on above code explain me how can I access a field of a singleton. I am not sure if my approach is correct. If I have singleton class and I want to use this MediaPlayer instance how do I do that?

Thanks!

Answer 1

Add null check for mp object which you are creating on playSound Button click :

public void playSound(View view){
    if(player.mp==null)
      player.mp = MediaPlayer.create(getApplicationContext(), R.raw.sound);
      player.mp.start();
}

because you have created singleton class for MyMediaPlayer class which avoid creating new object when player is already available. but mp is initialized every time.

EDIT: For playing multiple sound using single MediaPlayer do it as:

if(player.mp ==null)
  player.mp = new MediaPlayer();
else
  player.mp.reset();
String fileName="android.resource://"+getPackageName()+
                                               "/"+ R.raw.sound;
player.mp.setDataSource(getApplicationContext(),Uri.parse(fileName));
player.mp.prepare();
player.mp.start();