Set lock screen background in Android (like Spotify do)

Question

I know that this topic has been already discussed here, here and here, and the answer seems to be that it is not possible.

But I recently installed Spotify in my Nexus 4 (4.4.2), and it seems to be possible. When I listen a song in Spotify the lock screen background change with the cover of the album that I'm listening (see screenshots).

My theory was: when the phone is locked they change the phone wallpaper with the album cover in order to change also the lock screen background, then they set back the previous one when the phone is unlocked. But this is not how they do it, because in the permissions list of Spotify there is no "android.permission.SET_WALLPAPER"... :(

How do they do it? Some theory?

Answer 1

Edit: The solution below only works for applications that have registered itself as a media controller, so apps that don't play audio can't/shouldn't use this mechanism to change the lockscreen wallpaper.

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It can be done using RemoteControlClient, part of Android since ICS. If you want a working example, download VLC for Android and check out org.videolan.vlc.AudioService:

This part of the code is to intercept media controls.

/**  * Set up the remote control and tell the system we want to be the default receiver for the MEDIA buttons  * @see http://android-developers.blogspot.fr/2010/06/allowing-applications-to-play-nicer.html  */ @TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH) public void setUpRemoteControlClient() {     Context context = VLCApplication.getAppContext();     AudioManager audioManager = (AudioManager)context.getSystemService(AUDIO_SERVICE);      if(Util.isICSOrLater()) {         audioManager.registerMediaButtonEventReceiver(mRemoteControlClientReceiverComponent);          if (mRemoteControlClient == null) {             Intent mediaButtonIntent = new Intent(Intent.ACTION_MEDIA_BUTTON);             mediaButtonIntent.setComponent(mRemoteControlClientReceiverComponent);             PendingIntent mediaPendingIntent = PendingIntent.getBroadcast(context, 0, mediaButtonIntent, 0);              // create and register the remote control client             mRemoteControlClient = new RemoteControlClient(mediaPendingIntent);             audioManager.registerRemoteControlClient(mRemoteControlClient);         }          mRemoteControlClient.setTransportControlFlags(                 RemoteControlClient.FLAG_KEY_MEDIA_PLAY |                 RemoteControlClient.FLAG_KEY_MEDIA_PAUSE |                 RemoteControlClient.FLAG_KEY_MEDIA_PREVIOUS |                 RemoteControlClient.FLAG_KEY_MEDIA_NEXT |                 RemoteControlClient.FLAG_KEY_MEDIA_STOP);     } else if (Util.isFroyoOrLater()) {         audioManager.registerMediaButtonEventReceiver(mRemoteControlClientReceiverComponent);     } } 

This part is to update artwork, among other info:

@TargetApi(Build.VERSION_CODES.ICE_CREAM_SANDWICH) private void updateRemoteControlClientMetadata() {     if(!Util.isICSOrLater()) // NOP check         return;      if (mRemoteControlClient != null) {         MetadataEditor editor = mRemoteControlClient.editMetadata(true);         editor.putString(MediaMetadataRetriever.METADATA_KEY_ALBUM, getCurrentMedia().getAlbum());         editor.putString(MediaMetadataRetriever.METADATA_KEY_ARTIST, getCurrentMedia().getArtist());         editor.putString(MediaMetadataRetriever.METADATA_KEY_GENRE, getCurrentMedia().getGenre());         editor.putString(MediaMetadataRetriever.METADATA_KEY_TITLE, getCurrentMedia().getTitle());         editor.putLong(MediaMetadataRetriever.METADATA_KEY_DURATION, getCurrentMedia().getLength());         editor.putBitmap(MetadataEditor.BITMAP_KEY_ARTWORK, getCover());         editor.apply();     } } 

Answer 2

For me, the most instructive example was Random Music Player, mentioned in documentation about Android 4.0 APIs:

"For a sample implementation, see the Random Music Player, which provides compatibility logic such that it enables the remote control client on Android 4.0 devices while continuing to support devices back to Android 2.1."

In addition, I converted text to bitmap to have text as album art.