What are the correct arguments for requestaudiofocus?

Question

I am new to Android and Java. I have been working with the MediaPlayer and AudioManager examples provided by the Android Developer and other websites.

What I have noticed is that for the call to requestAudioFocus() there seems to be two separate signatures that are used. For example, from the http://developer.android.com/guide/topics/media/mediaplayer.html site there is:

AudioManager audioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
int result = audioManager.requestAudioFocus(this, AudioManager.STREAM_MUSIC,
    AudioManager.AUDIOFOCUS_GAIN);

if (result != AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
    // could not get audio focus.
}

With the following text:

"The first parameter to requestAudioFocus() is an AudioManager.OnAudioFocusChangeListener, whose onAudioFocusChange() method is called whenever there is a change in audio focus. Therefore, you should also implement this interface on your service and activities. For example:" (With the following code:)

class MyService extends Service
                implements AudioManager.OnAudioFocusChangeListener {
    // ....
    public void onAudioFocusChange(int focusChange) {
        // Do something based on focus change...
    }
}

Then from the site: http://developer.android.com/training/managing-audio/audio-focus.html there is:

OnAudioFocusChangeListener afChangeListener = new OnAudioFocusChangeListener() {
    public void onAudioFocusChange(int focusChange) {
        if (focusChange == AUDIOFOCUS_LOSS_TRANSIENT) {
            // Pause playback
        } else if (focusChange == AudioManager.AUDIOFOCUS_GAIN) {
            // Resume playback 
        } else if (focusChange == AudioManager.AUDIOFOCUS_LOSS) {
            am.unregisterMediaButtonEventReceiver(RemoteControlReceiver);
            am.abandonAudioFocus(afChangeListener);
            // Stop playback
        }
    }
};

AudioManager am = mContext.getSystemService(Context.AUDIO_SERVICE);
...

// Request audio focus for playback
int result = am.requestAudioFocus(afChangeListener,
                                 // Use the music stream.
                                 AudioManager.STREAM_MUSIC,
                                 // Request permanent focus.
                                 AudioManager.AUDIOFOCUS_GAIN);

if (result == AudioManager.AUDIOFOCUS_REQUEST_GRANTED) {
    am.registerMediaButtonEventReceiver(RemoteControlReceiver);
    // Start playback.
}

I've seen this dichotomy across numerous sites giving sample code for handling changes in audio focus. My understanding is that "this" provides context of the application's current state. I do not understand why in some cases "this" is the correct parameter while in other cases a handle to a change listener is the correct parameter when calling requestAudioFocus().

In fact the first example I provided states the first parameter should be an AudioManager.OnAudioFocusChangeListener. But "this" is used.

If you could explain why "this" is used instead of an AudioManager.OnAudioFocusChangeListener is used as a parameter it would be greatly appreciated.

Answer 1

It always takes an onAudioFocusedChangeListener. In the cases where this is passed, the current class implements the onAudioFocusChangeListener interface.