Based into Nathan's, adi's and swooby's code I created a full working example with some minor improvements.
Looking to the AudioFragment class we can see how easy is to listen for volume changes with our custom ContentObserver.
public class AudioFragment extends Fragment implements OnAudioVolumeChangedListener {
private AudioVolumeObserver mAudioVolumeObserver;
@Override
public void onResume() {
super.onResume();
// initialize audio observer
if (mAudioVolumeObserver == null) {
mAudioVolumeObserver = new AudioVolumeObserver(getActivity());
}
/*
* register audio observer to identify the volume changes
* of audio streams for music playback.
*
* It is also possible to listen for changes in other audio stream types:
* STREAM_RING: phone ring, STREAM_ALARM: alarms, STREAM_SYSTEM: system sounds, etc.
*/
mAudioVolumeObserver.register(AudioManager.STREAM_MUSIC, this);
}
@Override
public void onPause() {
super.onPause();
// release audio observer
if (mAudioVolumeObserver != null) {
mAudioVolumeObserver.unregister();
}
}
@Override
public void onAudioVolumeChanged(int currentVolume, int maxVolume) {
Log.d("Audio", "Volume: " + currentVolume + "/" + maxVolume);
Log.d("Audio", "Volume: " + (int) ((float) currentVolume / maxVolume) * 100 + "%");
}
}
public class AudioVolumeContentObserver extends ContentObserver {
private final OnAudioVolumeChangedListener mListener;
private final AudioManager mAudioManager;
private final int mAudioStreamType;
private int mLastVolume;
public AudioVolumeContentObserver(
@NonNull Handler handler,
@NonNull AudioManager audioManager,
int audioStreamType,
@NonNull OnAudioVolumeChangedListener listener) {
super(handler);
mAudioManager = audioManager;
mAudioStreamType = audioStreamType;
mListener = listener;
mLastVolume = audioManager.getStreamVolume(mAudioStreamType);
}
/**
* Depending on the handler this method may be executed on the UI thread
*/
@Override
public void onChange(boolean selfChange, Uri uri) {
if (mAudioManager != null && mListener != null) {
int maxVolume = mAudioManager.getStreamMaxVolume(mAudioStreamType);
int currentVolume = mAudioManager.getStreamVolume(mAudioStreamType);
if (currentVolume != mLastVolume) {
mLastVolume = currentVolume;
mListener.onAudioVolumeChanged(currentVolume, maxVolume);
}
}
}
@Override
public boolean deliverSelfNotifications() {
return super.deliverSelfNotifications();
}
}
public class AudioVolumeObserver {
private final Context mContext;
private final AudioManager mAudioManager;
private AudioVolumeContentObserver mAudioVolumeContentObserver;
public AudioVolumeObserver(@NonNull Context context) {
mContext = context;
mAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
}
public void register(int audioStreamType,
@NonNull OnAudioVolumeChangedListener listener) {
Handler handler = new Handler();
// with this handler AudioVolumeContentObserver#onChange()
// will be executed in the main thread
// To execute in another thread you can use a Looper
// +info: https://mcmap.net/q/89635/-contentobserver-onchange
mAudioVolumeContentObserver = new AudioVolumeContentObserver(
handler,
mAudioManager,
audioStreamType,
listener);
mContext.getContentResolver().registerContentObserver(
android.provider.Settings.System.CONTENT_URI,
true,
mAudioVolumeContentObserver);
}
public void unregister() {
if (mAudioVolumeContentObserver != null) {
mContext.getContentResolver().unregisterContentObserver(mAudioVolumeContentObserver);
mAudioVolumeContentObserver = null;
}
}
}
public interface OnAudioVolumeChangedListener {
void onAudioVolumeChanged(int currentVolume, int maxVolume);
}
Hope it's still useful for someone! :)
