Android 监听系统音量

/**
 * 媒体音量监听类
 */
public class VolumeChangeObserver {
     
    private static final String ACTION_VOLUME_CHANGED = "android.media.VOLUME_CHANGED_ACTION";
    private static final String EXTRA_VOLUME_STREAM_TYPE = "android.media.EXTRA_VOLUME_STREAM_TYPE";

    private Context mContext;
    private OnVolumeChangeListener mOnVolumeChangeListener;
    private VolumeReceiver mVolumeReceiver;
    private AudioManager mAudioManager;

    public VolumeChangeObserver(Context context) {
     
        mContext = context;
        mAudioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
    }

    public int getCurrentVolume() {
     
        return mAudioManager.getStreamVolume(AudioManager.STREAM_MUSIC);
    }

    public void registerVolumeReceiver() {
     
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(ACTION_VOLUME_CHANGED);
        mVolumeReceiver = new VolumeReceiver(this);
        mContext.registerReceiver(mVolumeReceiver, intentFilter);
    }

    public void unregisterVolumeReceiver() {
     
        if (mVolumeReceiver != null) mContext.unregisterReceiver(mVolumeReceiver);
        mOnVolumeChangeListener = null;
    }

    public void setOnVolumeChangeListener(OnVolumeChangeListener listener) {
     
        this.mOnVolumeChangeListener = listener;
    }

    public interface OnVolumeChangeListener {
     
        void onVolumeChange(int volume);
    }

    private static class VolumeReceiver extends BroadcastReceiver {
     
        private WeakReference<VolumeChangeObserver> mObserver;

        VolumeReceiver(VolumeChangeObserver observer) {
     
            mObserver = new WeakReference<>(observer);
        }

        @Override
        public void onReceive(Context context, Intent intent) {
     
            if (mObserver == null) return;
            if (mObserver.get().mOnVolumeChangeListener == null) return;
            if (isReceiveVolumeChange(intent)) {
     
                OnVolumeChangeListener listener = mObserver.get().mOnVolumeChangeListener;
                listener.onVolumeChange(mObserver.get().getCurrentVolume());
            }
        }

        private boolean isReceiveVolumeChange(Intent intent) {
     
            return intent.getAction() != null
                    && intent.getAction().equals(ACTION_VOLUME_CHANGED)
                    && intent.getIntExtra(EXTRA_VOLUME_STREAM_TYPE, -1) == AudioManager.STREAM_MUSIC;
        }
    }
}