Using ForwardingPlayer in MusicService

[marekkondracki]

I'm tried to set new ForwardingPlayer with custom callbacks in my project, but it didn't work. So I tried with UAMP project. It also didn't work.

I swapped code, according to 2.16.0 release notes, in this file: MusicService.kt

mediaSessionConnector.setPlayer(newPlayer)

with:

        mediaSessionConnector.setPlayer(object : ForwardingPlayer(newPlayer) {
            override fun prepare() {
                super.prepare()
                Log.i(TAG, "prepare")
            }

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

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

            override fun getSeekBackIncrement() = 12000L

            override fun getSeekForwardIncrement() = 18000L
        }
        )

No one of callbacks above never fired. I can't find any information about how to use ForwardingExoplayer.

[marcbaechinger]

The ForwardingPlayeras a class is working fine, if it gets called. I used it various times. It may be that it is not called if you create an anonymous inner class as above for the MediaSessionConnector exclusively.

Are you sure that the commands arrive through the MediaSession? In UAMP for example it could be that a command comes from a PendingIntent of the notification manager. If this is the case, the ForwardingPlayer that you pass to mediaSessionConnector.setPlayer() would not be called. In the case of UAMP you want to look for notificationManager.showNotificationForPlayer(currentPlayer) as well.

So probably this makes the forwarding player being called:

Player forwardingPlayer = new ForwardingPlayer(player);

mediaSessionConnector.setPlayer(forwardingPlayer);
notificationManager.showNotificationForPlayer(forwardingPlayer)

[marekkondracki]

So I pass ForwardingPlayer by:

mediaSessionConnector?.setPlayer(CustomForwardingPlayer((currentPlayer)))
playerNotificationManager?.setPlayer(CustomForwardingPlayer((currentPlayer)))

After click seek forward on notification, callback seekForward() in ForwardingPlayer was fired, but getSeekForwardIncrement() did not. I checked ExoPlayer sources and assumed that only external calls on ForwardingPlayer, from mediaSessionConnector or notificationManager will work cause they pass through ForwardingPlayer.

I assumed that ExoPlayer.Builder() returns SimpleExoPlayer which is ExoPlayerImpl() and method getSeekForwardIncrement() returns value passed by ExoPlayerImpl constructor, not ForwardingPlayer.

Before 2.16.0, I used DefaultControlDispatcher in case, I want to change seek/forward values dynamically, I just passplayerNotificationManager.setControlDispatcher(defaultDispatcher).

Do now I need to build new ExoPlayer every time I want to change these values?

[marcbaechinger]

No, you don't need to build ExoPlayer each time when you change the increment.

But you are right this is confusing and we need at least to document this properly on the ForwardingPlayer because I think it is quite likely that other people make the same assumption. You actually hit a special case where two methods depend on each other and this is not ideal for the delegation that ForwardingPlayer is implemented.

Let me explain in more detail:

The ForwardingPlayer is using composition and delegates all calls to the player that you pass to the constructor. When now seekBack() is called and delegated to the player, then that player uses the result of getSeekBackIncrement() of that player to get the seek increment. It never asks the ForwardingPlayer due to how this is implemented. Instead when you attempt to change the seek increment you need to override both method. This isn't clear and needs at least to be documented clearly on ForwardingPlayer.getSeekBackIncrement() and ForwardingPlayer.getSeekForwardIncrement().

What you want to achieve probably could look like this in code:

    ForwardingPlayer forwardingPlayer = new ForwardingPlayer(player) {

      long seekBackIncrement = 3_000; // 3 seconds
      long seekForwardIncrement = 20_000; // 20 seconds

      public void setSeekBackIncrement(long seekBackIncrement) {
        this.seekBackIncrement = seekBackIncrement;
      }

      public void setSeekForwardIncrement(long seekForwardIncrement) {
        this.seekForwardIncrement = seekForwardIncrement;
      }
      
      @Override
      public long getSeekBackIncrement() {
        return seekBackIncrement;
      }

      @Override
      public void seekBack() {
        seekToOffset(-seekBackIncrement);
      }

      @Override
      public long getSeekForwardIncrement() {
        return seekForwardIncrement;
      }

      @Override
      public void seekForward() {
        seekToOffset(seekForwardIncrement);
      }

      private void seekToOffset(long offsetMs) {
        long positionMs = getCurrentPosition() + offsetMs;
        long durationMs = getDuration();
        if (durationMs != C.TIME_UNSET) {
          positionMs = min(positionMs, durationMs);
        }
        positionMs = max(positionMs, 0);
        seekTo(positionMs);
      }
    };

I marked this issue as a documentation candidate.

[marekkondracki]

Thank you for clear explanation and fast response!