Android(安卓)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;        }    }}
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