flutter - audio_serviceフラッターでプレイリストから特定のキュー位置メディアアイテムを渡して再生する方法は?

Question

音楽プレーヤーにflutter audio_serviceとjust_audioパッケージを使用しています。音楽プレーヤーを初期化するときに、プレイリストから特定のキュー位置のメディア アイテムを再生したいと考えています。AudioService.start() メソッドを呼び出すと、常にプレイリストの最初のアイテムが再生されます。オーディオ サービスを開始するときに、特定のキュー位置のメディア アイテムをプレイリストから渡して再生するにはどうすればよいですか?

AudioService 開始

AudioService.start(
        backgroundTaskEntrypoint: _audioPlayerTaskEntrypoint,
        androidNotificationChannelName: 'Zenmind',
        androidNotificationColor: 0xFF2196f3,
        androidNotificationIcon: 'mipmap/ic_launcher',
        androidEnableQueue: true,
        params: params); // [params contains playlist ] 

_audioPlayerTaskエントリポイント コード

void _audioPlayerTaskEntrypoint() async {
  AudioServiceBackground.run(() => AudioPlayerTask());
}

AudioPlayerTask クラス

class AudioPlayerTask extends BackgroundAudioTask {
  var _queue = <MediaItem>[];
  AudioPlayer _player = new AudioPlayer();
  AudioProcessingState _skipState;
  Seeker _seeker;
  StreamSubscription<PlaybackEvent> _eventSubscription;

  List<MediaItem> get queue => _queue;
  int get index => _player.currentIndex;
  MediaItem get mediaItem => index == null ? null : queue[index];

  @override
  Future<void> onStart(Map<String, dynamic> params) async {
    _queue.clear();
    List mediaItems = params['data'];
    // print(params['data']);
    for (int i = 0; i < mediaItems.length; i++) {
      MediaItem mediaItem = MediaItem.fromJson(mediaItems[i]);
      _queue.add(mediaItem);
    }

    _player.currentIndexStream.listen((index) {
      print("index value is $index");
      if (index != null) {
        AudioServiceBackground.setMediaItem(queue[index]);
      }
    });
    _eventSubscription = _player.playbackEventStream.listen((event) {
      _broadcastState();
    });

    _player.processingStateStream.listen((state) {
      switch (state) {
        case ProcessingState.completed:
          onStop();
          break;
        case ProcessingState.ready:
          _skipState = null;
          break;
        default:
          break;
      }
    });

    AudioServiceBackground.setQueue(queue);
    try {
      await _player.setAudioSource(ConcatenatingAudioSource(
        children:
            queue.map((item) => AudioSource.uri(Uri.parse(item.id))).toList(),
      ));
      onSkipToQueueItem(queue[1].id);
      onPlay();
    } catch (e) {
      print("Error: $e");
      onStop();
    }
  }

  @override
  Future<void> onSkipToQueueItem(String mediaId) async {
    final newIndex = queue.indexWhere((item) => item.id == mediaId);
    if (newIndex == -1) return;
    _skipState = newIndex > index
        ? AudioProcessingState.skippingToNext
        : AudioProcessingState.skippingToPrevious;
    _player.seek(Duration.zero, index: newIndex);
    AudioServiceBackground.sendCustomEvent('skip to $newIndex');
  }

  @override
  Future<void> onPlay() => _player.play();

  @override
  Future<void> onPause() => _player.pause();

  @override
  Future<void> onSeekTo(Duration position) => _player.seek(position);

  @override
  Future<void> onFastForward() => _seekRelative(fastForwardInterval);

  @override
  Future<void> onRewind() => _seekRelative(-rewindInterval);

  @override
  Future<void> onSeekForward(bool begin) async => _seekContinuously(begin, 1);

  @override
  Future<void> onSeekBackward(bool begin) async => _seekContinuously(begin, -1);

  @override
  Future<void> onStop() async {
    await _player.dispose();
    _eventSubscription.cancel();
    await _broadcastState();
    await super.onStop();
  }

  Future<void> _seekRelative(Duration offset) async {
    var newPosition = _player.position + offset;
    if (newPosition < Duration.zero) newPosition = Duration.zero;
    if (newPosition > mediaItem.duration) newPosition = mediaItem.duration;
    // if (newPosition > _player.duration) newPosition = _player.duration;
    await _player.seek(newPosition);
  }

  void _seekContinuously(bool begin, int direction) {
    _seeker?.stop();
    if (begin) {
      _seeker = Seeker(
          _player,
          Duration(seconds: 10 * direction),
          // Duration(seconds: 1), mediaItem)
          Duration(seconds: 1),
          queue[_player.currentIndex])
        ..start();
    }
  }

  Future<void> _broadcastState() async {
    await AudioServiceBackground.setState(
      controls: [
        MediaControl.skipToPrevious,
        if (_player.playing) MediaControl.pause else MediaControl.play,
        MediaControl.stop,
        MediaControl.skipToNext,
      ],
      systemActions: [
        MediaAction.seekTo,
        MediaAction.seekForward,
        MediaAction.seekBackward,
      ],
      androidCompactActions: [0, 1, 3],
      processingState: _getProcessingState(),
      playing: _player.playing,
      position: _player.position,
      bufferedPosition: _player.bufferedPosition,
      speed: _player.speed,
    );
  }

  AudioProcessingState _getProcessingState() {
    if (_skipState != null) return _skipState;
    switch (_player.processingState) {
      case ProcessingState.idle:
        return AudioProcessingState.stopped;
      case ProcessingState.loading:
        return AudioProcessingState.connecting;
      case ProcessingState.buffering:
        return AudioProcessingState.buffering;
      case ProcessingState.ready:
        return AudioProcessingState.ready;
      case ProcessingState.completed:
        return AudioProcessingState.completed;
      default:
        throw Exception("Invalid state: ${_player.processingState}");
    }
  }
}