I know how to listen to volume buttons in an activity. But can I do that in a background service? If yes, how to do that?

Solution 1

It is possible. Use code below (for newer Android versions, especially Marshmallow, see bottom of the answer):

public class SettingsContentObserver extends ContentObserver {
    int previousVolume;
    Context context;

    public SettingsContentObserver(Context c, Handler handler) {
        super(handler);
        context=c;

        AudioManager audio = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
        previousVolume = audio.getStreamVolume(AudioManager.STREAM_MUSIC);
    }

    @Override
    public boolean deliverSelfNotifications() {
        return super.deliverSelfNotifications();
    }

    @Override
    public void onChange(boolean selfChange) {
        super.onChange(selfChange);

        AudioManager audio = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);
        int currentVolume = audio.getStreamVolume(AudioManager.STREAM_MUSIC);

        int delta=previousVolume-currentVolume;

        if(delta>0)
        {
            Logger.d("Ściszył!"); // volume decreased.
            previousVolume=currentVolume;
        }
        else if(delta<0)
        {
            Logger.d("Zrobił głośniej!"); // volume increased.
            previousVolume=currentVolume;
        }
    }
}

Then in your service onCreate register it with:

mSettingsContentObserver = new SettingsContentObserver(this,new Handler());
getApplicationContext().getContentResolver().registerContentObserver(android.provider.Settings.System.CONTENT_URI, true, mSettingsContentObserver );

Then unregister in onDestroy:

getApplicationContext().getContentResolver().unregisterContentObserver(mSettingsContentObserver);

Note that this example judges by change of media volume, if you want to use other volume, change it!

UPDATE:

Above method supposedly doesn't work on Marshmallow, BUT there's much better way now since MediaSession was introduced! So first you have to migrate your code to MediaController/MediaSession pattern and then use this code:

private VolumeProviderCompat myVolumeProvider = null;

myVolumeProvider = new VolumeProviderCompat(VolumeProviderCompat.VOLUME_CONTROL_RELATIVE, maxVolume, currentVolume) {
    @Override
    public void onAdjustVolume(int direction) {
        // <0 volume down
        // >0 volume up

    }
};

mSession.setPlaybackToRemote(myVolumeProvider);

Somehow volume button presses are detected even with screen off (just be sure to register proper media button intent receiver if applicable for your platform!)

UPDATE 2 since GalDude requested some more info on getting media MediaSession/MediaController. Sorry, but since I stopped using Java it will be in Kotlin:

lateinit var mediaSession: MediaSessionCompat // you have to initialize it in your onCreate method
val kontroler: MediaControllerCompat
 get() = mediaSession.controller // in Java it's just getController() on mediaSession

// in your onCreate/start method:
mediaSession = MediaSessionCompat(this, "YourPlayerName", receiver, null)
mediaSession.setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS or MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS)
mediaSession.isActive = true
if (ratingIsWorking) // note: rating crashes on some machines you have to check it!
    mediaSession.setRatingType(RatingCompat.RATING_5_STARS)

mediaSession.setCallback(object : MediaSessionCompat.Callback() {
...
// here you have to implement what happens with your player when play/pause/stop/ffw etc. is requested - see exaples elsewhere
})

// onDestroy/exit method:
mediaSession.isActive = false
mediaSession.release()

Solution 2

The AOSP Music app has a Service (MediaPlaybackService) that responds to volume key events by registering a BroadcastReceiver (MediaButtonIntentReceiver).

Here's the code snippet where it registers the receiver:

    mAudioManager = (AudioManager) getSystemService(Context.AUDIO_SERVICE);
    ComponentName rec = new ComponentName(getPackageName(),
            MediaButtonIntentReceiver.class.getName());
    mAudioManager.registerMediaButtonEventReceiver(rec);

Also, don't forget about manifest:

    <receiver android:name="com.android.music.MediaButtonIntentReceiver">
        <intent-filter>
            <action android:name="android.intent.action.MEDIA_BUTTON" />
            <action android:name="android.media.AUDIO_BECOMING_NOISY" />
        </intent-filter>
    </receiver>

This works even if the Music app is not in the foreground. Isn't that what you want?

Solution 3

Unfortunately, this is another area of Android where there are like five different ways to "solve the problem", but most of them don't work very well. For my own sanity, I'll attempt to list all the different approaches below.

Solutions

1) MediaSession (from Service)

Answer by Denis Kniazhev: https://stackoverflow.com/a/43304591/2441655

Drawbacks:

  1. Requires Android API level 21+ (Android 5.0+).

2) android.media.VOLUME_CHANGED_ACTION (from Service)

Answer by Nikhil: https://stackoverflow.com/a/44040282/2441655

Drawbacks:

  1. Not an official part of the SDK: https://stackoverflow.com/a/8974510/2441655
  2. Ignores first-press of volume-key (since it only shows the volume-bar).
  3. Ignores volume-up key when at 100%, and volume-down key when at 0%.

3) ContentObserver (from Service)

Answer by ssuukk: https://stackoverflow.com/a/15292255/2441655 (first part)

Drawbacks:

  1. Doesn't work in newer versions of Android: comment by dsemi
  2. Ignores first-press of volume-key (since it only shows the volume-bar).
  3. Ignores volume-up key when at 100%, and volume-down key when at 0%.

4) AudioManager.registerMediaButtonEventReceiver (from Service)

Answer by Joe: https://stackoverflow.com/a/11510564/2441655

Drawbacks:

  1. Doesn't work on most roms: comment by elgui

5) onKeyDown (from Activity)

Answer by dipali: https://stackoverflow.com/a/21086563/2441655

Drawbacks:

  1. Doesn't work if screen is off, in different app, etc.

6) dispatchKeyEvent (from Activity)

Answer by Maurice Gavin: https://stackoverflow.com/a/11462962/2441655

Drawbacks:

  1. Doesn't work if screen is off, in different app, etc.

Conclusion

The solution I'm currently using is #1, because:

  1. It's an official part of the SDK.
  2. It is usable from a service. (ie. regardless of what app you're in)
  3. It captures every volume-key press, regardless of current-volume/ui-state.
  4. It works when the screen is off.

Let me know if you find any others -- or if you've found more drawbacks to some of them!

Solution 4

I was able to make it work on android 5+ devices using MediaSession. However,ContentObserver suggested by @ssuukk didn't work for me on both 4.4 and 7.0 devices (at least on ROMs that I've been testing on). Here is a full example which works on android 5+.

Service:

import android.app.Service;
import android.content.Intent;
import android.os.IBinder;
import android.support.v4.media.VolumeProviderCompat;
import android.support.v4.media.session.MediaSessionCompat;
import android.support.v4.media.session.PlaybackStateCompat;

public class PlayerService extends Service {
    private MediaSessionCompat mediaSession;

    @Override
    public void onCreate() {
        super.onCreate();
        mediaSession = new MediaSessionCompat(this, "PlayerService");
        mediaSession.setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS |
                MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS);
        mediaSession.setPlaybackState(new PlaybackStateCompat.Builder()
                .setState(PlaybackStateCompat.STATE_PLAYING, 0, 0) //you simulate a player which plays something.
                .build());

        //this will only work on Lollipop and up, see https://code.google.com/p/android/issues/detail?id=224134
        VolumeProviderCompat myVolumeProvider =
                new VolumeProviderCompat(VolumeProviderCompat.VOLUME_CONTROL_RELATIVE, /*max volume*/100, /*initial volume level*/50) {
            @Override
            public void onAdjustVolume(int direction) {
                /*
                -1 -- volume down
                1 -- volume up
                0 -- volume button released
                 */
            }
        };

        mediaSession.setPlaybackToRemote(myVolumeProvider);
        mediaSession.setActive(true);
    }


    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        mediaSession.release();
    }
}

In AndroidManifest.xml:

<application ...>
    ...
    <service android:name=".PlayerService"/>
</application>

In your activity:

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    ...
    startService(new Intent(this, PlayerService.class));
}

There are several things to be aware of:

  • It intercepts volume buttons completely so while this code is running you won't be able to adjust ring volume using volume buttons. This might be possible to fix, I just didn't try.
  • If you run the example as-is the volume buttons will remain controlled by the app even when the screen is off and the app has been removed from "Recent Apps" list. You'll have to go to Settings->Applications, find the app and force stop it to get volume buttons back.

Solution 5

Judging by the couple of other questions about this topic, no.

Other question 1, Other question 2

Services simply do not receive KeyEvent callbacks.

Solution 6

You need to play blank sound from service then only you can listen to volume changes. Following worked for me

Steps

1. Put blank.mp3 in raw folder (Download from here)

2. Start media at onStartCommand()

private MediaPlayer mediaPlayer;

public MyService() {
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {

    ........

    mediaPlayer = MediaPlayer.create(this, R.raw.blank);
    mediaPlayer.setLooping(true);
    mediaPlayer.start();

    .......

    return START_STICKY;
}

3. You must choose to stop and release mediaplayer. It's better to do so in onDestroy()

@Override
public void onDestroy() {

    mediaPlayer.stop();
    mediaPlayer.release();

    super.onDestroy();
}

4. Create Broadcast receiver that will listen for volume changes

int volumePrev = 0;

private BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
    @Override
    public void onReceive(Context context, Intent intent) {

        if ("android.media.VOLUME_CHANGED_ACTION".equals(intent.getAction())) {

            int volume = intent.getIntExtra("android.media.EXTRA_VOLUME_STREAM_VALUE",0);

            Log.i(TAG, "volume = " + volume);

            if (volumePrev  < volume) {
                Log.i(TAG, "You have pressed volume up button");
            } else {
                Log.i(TAG, "You have pressed volume down button");
            }
            volumePrev = volume;
        }
    }
};

5. Register the broadcast receiver in onStartCommand()

@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    .....

    IntentFilter filter = new IntentFilter();
    filter.addAction("android.media.VOLUME_CHANGED_ACTION");
    registerReceiver(broadcastReceiver, filter);

    ....

    return START_STICKY;
}

6. Unregister broadccast receiver in onDestroy()

 @Override
public void onDestroy() {
    .....

    unregisterReceiver(broadcastReceiver);

    .....

    super.onDestroy();
}

That's all

Solution 7

This requires Lollipop (v5.0/API 21) or higher

My goal was to adjust system volume from a Service. Any action can be taken on press though.

public class VolumeKeyController {

    private MediaSessionCompat mMediaSession;
    private final Context mContext;

    public VolumeKeyController(Context context) {
        mContext = context;
    }

    private void createMediaSession() {
        mMediaSession = new MediaSessionCompat(mContext, KeyUtil.log);

        mMediaSession.setFlags(MediaSessionCompat.FLAG_HANDLES_MEDIA_BUTTONS |
                MediaSessionCompat.FLAG_HANDLES_TRANSPORT_CONTROLS);
        mMediaSession.setPlaybackState(new Builder()
                .setState(PlaybackStateCompat.STATE_PLAYING, 0, 0)
                .build());
        mMediaSession.setPlaybackToRemote(getVolumeProvider());
        mMediaSession.setActive(true);
    }

    private VolumeProviderCompat getVolumeProvider() {
        final AudioManager audio = mContext.getSystemService(Context.AUDIO_SERVICE);

        int STREAM_TYPE = AudioManager.STREAM_MUSIC;
        int currentVolume = audio.getStreamVolume(STREAM_TYPE);
        int maxVolume = audio.getStreamMaxVolume(STREAM_TYPE);
        final int VOLUME_UP = 1;
        final int VOLUME_DOWN = -1;

        return new VolumeProviderCompat(VolumeProviderCompat.VOLUME_CONTROL_RELATIVE, maxVolume, currentVolume) {
            @Override
            public void onAdjustVolume(int direction) {
                // Up = 1, Down = -1, Release = 0
                // Replace with your action, if you don't want to adjust system volume
                if (direction == VOLUME_UP) {
                    audio.adjustStreamVolume(STREAM_TYPE,
                            AudioManager.ADJUST_RAISE, AudioManager.FLAG_REMOVE_SOUND_AND_VIBRATE);
                }
                else if (direction == VOLUME_DOWN) {
                    audio.adjustStreamVolume(STREAM_TYPE,
                            AudioManager.ADJUST_LOWER, AudioManager.FLAG_REMOVE_SOUND_AND_VIBRATE);
                }
                setCurrentVolume(audio.getStreamVolume(STREAM_TYPE));
            }
        };
    }

    // Call when control needed, add a call to constructor if needed immediately
    public void setActive(boolean active) {
        if (mMediaSession != null) {
            mMediaSession.setActive(active);
            return;
        }
        createMediaSession();
    }

    // Call from Service's onDestroy method
    public void destroy() {
        if (mMediaSession != null) {
            mMediaSession.release();
        }
    }
}

Solution 8

@venryx: Solution 1 no longer works in Android 12
@ssuukk: I can confirm @venryx's comment that SettingsContentObserver does not get triggered if the volume is already at min or max.
@bikram: I created a VolumeButtonHelper class that uses this approach. Although it does use an undocumented SDK feature, it still works in 2022. I have extensively researched this topic and this was the only solution I could find.

class VolumeButtonHelper(private var context: Context,
                         private var stream: Int? = null,
                         enabledScreenOff: Boolean)
{
  companion object
  {
    const val VOLUME_CHANGE_ACTION = "android.media.VOLUME_CHANGED_ACTION"
    const val EXTRA_VOLUME_STREAM_TYPE = "android.media.EXTRA_VOLUME_STREAM_TYPE"
  }

  enum class Direction
  {
    Up,
    Down,
    Release
  }

  private lateinit var mediaPlayer: MediaPlayer
  private var volumeBroadCastReceiver: VolumeBroadCastReceiver? = null
  private var volumeChangeListener: VolumeChangeListener? = null

  private val audioManager: AudioManager? =
    context.getSystemService(Context.AUDIO_SERVICE) as? AudioManager

  private var priorVolume = -1
  private var volumePushes = 0.0
  private var longPressReported = false

  var doublePressTimeout = 350L
  var buttonReleaseTimeout = 100L

  var minVolume = -1
    private set

  var maxVolume = -1
    private set

  var halfVolume = -1
    private set

  var currentVolume = -1
    private set

  init
  {
    if (audioManager != null)
    {
      minVolume = audioManager.getStreamMinVolume(STREAM_MUSIC)
      maxVolume = audioManager.getStreamMaxVolume(STREAM_MUSIC)
      halfVolume = (minVolume + maxVolume) / 2

      /*************************************
       * BroadcastReceiver does not get triggered for VOLUME_CHANGE_ACTION
       * if the screen is off and no media is playing.
       * Playing a silent media file solves that.
       *************************************/
      if (enabledScreenOff)
      {
        mediaPlayer =
          MediaPlayer.create(context,
                             R.raw.silence)
            .apply {
              isLooping = true
              setWakeMode(context, PARTIAL_WAKE_LOCK)
              start()

            }
      }
    }
    else
      Log.e(TAG, "Unable to initialize AudioManager")

  }

  fun registerVolumeChangeListener(volumeChangeListener: VolumeChangeListener)
  {
    if (volumeBroadCastReceiver == null)
    {
      this.volumeChangeListener = volumeChangeListener
      volumeBroadCastReceiver = VolumeBroadCastReceiver()

      if (volumeBroadCastReceiver != null)
      {
        val filter = IntentFilter()
        filter.addAction(VOLUME_CHANGE_ACTION)

        context.registerReceiver(volumeBroadCastReceiver, filter)

      }
      else
        Log.e(TAG, "Unable to initialize BroadCastReceiver")

    }
  }

  fun unregisterReceiver()
  {
    if (volumeBroadCastReceiver != null)
    {
      context.unregisterReceiver(volumeBroadCastReceiver)
      volumeBroadCastReceiver = null

    }
  }

  fun onVolumePress(count: Int)
  {
    when (count)
    {
      1 -> volumeChangeListener?.onSinglePress()
      2 -> volumeChangeListener?.onDoublePress()
      else -> volumeChangeListener?.onVolumePress(count)

    }
  }

  interface VolumeChangeListener
  {
    fun onVolumeChange(direction: Direction)
    fun onVolumePress(count: Int)
    fun onSinglePress()
    fun onDoublePress()
    fun onLongPress()

  }

  inner class VolumeBroadCastReceiver : BroadcastReceiver()
  {
    override fun onReceive(context: Context, intent: Intent)
    {
      if (stream == null ||
          intent.getIntExtra(EXTRA_VOLUME_STREAM_TYPE, -1) == stream)
      {
        currentVolume = audioManager?.getStreamVolume(STREAM_MUSIC) ?: -1

        if (currentVolume != -1)
        {
          if (currentVolume != priorVolume)
          {
            if (currentVolume > priorVolume)
              volumeChangeListener?.onVolumeChange(Up)
            else if (currentVolume < priorVolume)
              volumeChangeListener?.onVolumeChange(Down)

            priorVolume = currentVolume

          }

          volumePushes += 0.5 // For some unknown reason (to me), onReceive gets called twice for every button push

          if (volumePushes == 0.5)
          {
            CoroutineScope(Dispatchers.Main).launch {
              delay(doublePressTimeout - buttonReleaseTimeout)
              buttonDown()

            }
          }
        }
      }
    }

    private fun buttonDown()
    {
      val startVolumePushes = volumePushes

      CoroutineScope(Dispatchers.Main).launch {
        delay(buttonReleaseTimeout)
        val currentVolumePushes = volumePushes

        if (startVolumePushes != currentVolumePushes)
        {
          if (volumePushes > 2 && !longPressReported)
          {
            longPressReported = true
            volumeChangeListener?.onLongPress()

          }

          buttonDown()

        }
        else
        {
          onVolumePress(volumePushes.toInt())
          volumeChangeListener?.onVolumeChange(Release)
          volumePushes = 0.0
          longPressReported = false

        }
      }
    }
  }
}

Instantiate that class in a Service (with the appropriate wake lock):

class ForegroundService : Service()
{
  private lateinit var volumeButtonHelper: VolumeButtonHelper

  companion object
  {
    var wakeLock: WakeLock? = null

    const val TAG = "VolumeButtonHelper"
    const val ACTION_FOREGROUND_WAKELOCK = "com.oliverClimbs.volumeButtonHelper.FOREGROUND_WAKELOCK"
    const val ACTION_FOREGROUND = "com.oliverClimbs.volumeButtonHelper.FOREGROUND"
    const val WAKELOCK_TAG = "com.oliverClimbs.volumeButtonHelper:wake-service"
    const val CHANNEL_ID = "Running in background"

  }

  override fun onBind(p0: Intent?): IBinder?
  {
    return null
  }

  override fun onCreate()
  {
    super.onCreate()

    volumeButtonHelper = VolumeButtonHelper(this,
                                            STREAM_MUSIC,
                                            enabledScreenOff = true)

    volumeButtonHelper.registerVolumeChangeListener(
      object : VolumeButtonHelper.VolumeChangeListener
      {
        override fun onVolumeChange(direction: VolumeButtonHelper.Direction)
        {
          Log.i(TAG, "onVolumeChange: $direction")
        }

        override fun onVolumePress(count: Int)
        {
          Log.i(TAG, "onVolumePress: $count")
        }

        override fun onSinglePress()
        {
          Log.i(TAG, "onSinglePress")
        }

        override fun onDoublePress()
        {
          Log.i(TAG, "onDoublePress")
        }

        override fun onLongPress()
        {
          Log.i(TAG, "onLongPress")
        }
      })
  }

  @SuppressLint("WakelockTimeout")
  override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int
  {
    super.onStartCommand(intent, flags, startId)

    if (intent?.action == ACTION_FOREGROUND || intent?.action == ACTION_FOREGROUND_WAKELOCK)
      startForeground(R.string.foreground_service_started,
                      Notification.Builder(this, CHANNEL_ID).build())

    if (intent?.action == ACTION_FOREGROUND_WAKELOCK)
    {
      if (wakeLock == null)
      {
        wakeLock = getSystemService(PowerManager::class.java)?.newWakeLock(
          PARTIAL_WAKE_LOCK,
          WAKELOCK_TAG)

        wakeLock?.acquire()

      }
      else
      {
        releaseWakeLock()

      }
    }

    return START_STICKY

  }

  private fun releaseWakeLock()
  {
    wakeLock?.release()
    wakeLock = null

  }

  override fun onDestroy()
  {
    super.onDestroy()
    releaseWakeLock()

    stopForeground(STOP_FOREGROUND_REMOVE)

    volumeButtonHelper.unregisterReceiver()

  }
}

Start the Service from your Activity:

class MainActivity : AppCompatActivity()
{
  private var configurationChange = false

  override fun onCreate(savedInstanceState: Bundle?)
  {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    if (!configurationChange)
      startService(Intent(ForegroundService.ACTION_FOREGROUND_WAKELOCK).setClass(this,
                                                                                 ForegroundService::class.java))

  }

  override fun onDestroy()
  {
    Log.d(TAG, "MainActivity: onDestroy")

    configurationChange =
      if (isChangingConfigurations)
        true
      else
      {
        stopService(Intent(this, ForegroundService::class.java))
        false

      }

    super.onDestroy()

  }
}

I have shared the full project at github.com/oliverClimbs/VolumeButtonDemo.

Solution 9

Android doesn't document APIs on interacting with volume buttons in that case. So I guess the answer is no

Solution 10

checkout Controlling Your Apps Volume and Playback ...This will help to solve your problem... multiple applications might want to listen for button presses from background, this may be the reason why KeyEvents can only be handled by Activities as they are the interface to the user pressing the keys.

Solution 11

Note: this only works for Activities, and not Services as the question states.

Depending on the context in which the callback is required an alternative solution might be available.

To be capable of detecting the volume button an Activity would need to override the dispatchKeyEvent function. For this to be present in multiple activities could could write a superclass containing the overridden function which is extended by all subsequent activities.

Here is the code for detecting Volume Up/Down key presses:

    // Over-ride this function to define what should happen when keys are pressed (e.g. Home button, Back button, etc.)
    @Override
    public boolean dispatchKeyEvent(KeyEvent event) 
    {
        if (event.getAction() == KeyEvent.ACTION_DOWN)
        {
            switch (event.getKeyCode()) 
            {
                case KeyEvent.KEYCODE_VOLUME_UP:
                    // Volume up key detected
                    // Do something
                    return true;
                case KeyEvent.KEYCODE_VOLUME_DOWN:
                    // Volume down key detected
                    // Do something
                    return true;
            }
        }

        return super.dispatchKeyEvent(event);
    }