Question

 await AudioService.start(
      backgroundTaskEntrypoint: _audioPlayerTaskEntrypoint,
      androidNotificationChannelName: 'Audio Player',
      androidNotificationColor: 0xFF2196f3,
      androidNotificationIcon: 'mipmap/ic_launcher',
      params: getParams(),
    );

这是我的代码段，我在其中调用AudioService.start，但无法启动服务。我正在从Firebase中获取音频项目，并希望将其作为列表视图加载到audio_service。。但是我无法做到这一点。在我定义了扩展后台服务的音频服务的我的课程中。


import 'package:audio_service/audio_service.dart';
import 'package:just_audio/just_audio.dart';

MediaControl playControl = MediaControl(
  androidIcon: 'drawable/ic_action_play_arrow',
  label: 'Play',
  action: MediaAction.play,
);
MediaControl pauseControl = MediaControl(
  androidIcon: 'drawable/ic_action_pause',
  label: 'Pause',
  action: MediaAction.pause,
);
MediaControl skipToNextControl = MediaControl(
  androidIcon: 'drawable/ic_action_skip_next',
  label: 'Next',
  action: MediaAction.skipToNext,
);
MediaControl skipToPreviousControl = MediaControl(
  androidIcon: 'drawable/ic_action_skip_previous',
  label: 'Previous',
  action: MediaAction.skipToPrevious,
);
MediaControl stopControl = MediaControl(
  androidIcon: 'drawable/ic_action_stop',
  label: 'Stop',
  action: MediaAction.stop,
);

class AudioPlayerTask extends BackgroundAudioTask {
  //
  var _queue = <MediaItem>[];

  int _queueIndex = -1;

  AudioPlayer _audioPlayer = new AudioPlayer();
  AudioProcessingState _skipState;
  bool _playing;

  bool get hasNext => _queueIndex + 1 < _queue.length;

  bool get hasPrevious => _queueIndex > 0;

  MediaItem get mediaItem => _queue[_queueIndex];

  StreamSubscription<AudioPlaybackState> _playerStateSubscription;
  StreamSubscription<AudioPlaybackEvent> _eventSubscription;

  @override
  void onStart(Map<String, dynamic> params) {
    print("-------------------------------------started");
    _queue.clear();
    List mediaItems = params['data'];
    for (int i = 0; i < mediaItems.length; i++) {
      MediaItem mediaItem = MediaItem.fromJson(mediaItems[i]);
      _queue.add(mediaItem);
    }
    _playerStateSubscription = _audioPlayer.playbackStateStream
        .where((state) => state == AudioPlaybackState.completed)
        .listen((state) {
      _handlePlaybackCompleted();
    });
    _eventSubscription = _audioPlayer.playbackEventStream.listen((event) {
      final bufferingState =
      event.buffering ? AudioProcessingState.buffering : null;
      switch (event.state) {
        case AudioPlaybackState.paused:
          _setState(
              processingState: bufferingState ?? AudioProcessingState.ready,
              position: event.position);
          break;
        case AudioPlaybackState.playing:
          _setState(
              processingState: bufferingState ?? AudioProcessingState.ready,
              position: event.position);
          break;
        case AudioPlaybackState.connecting:
          _setState(
              processingState: _skipState ?? AudioProcessingState.connecting,
              position: event.position);
          break;
        default:
      }
    });
    AudioServiceBackground.setQueue(_queue);
    onSkipToNext();
  }

  @override
  void onPlay() {
    if (_skipState == null) {
      _playing = true;
      _audioPlayer.play();
    }
  }

  @override
  void onPause() {
    _playing = false;
    _audioPlayer.pause();
  }

  @override
  void onSkipToNext() async {
    skip(1);
  }

  @override
  void onSkipToPrevious() {
    skip(-1);
  }

  void skip(int offset) async {
    int newPos = _queueIndex + offset;
    if (!(newPos >= 0 && newPos < _queue.length)) {
      return;
    }
    if (null == _playing) {
      _playing = true;
    } else if (_playing) {
      await _audioPlayer.stop();
    }
    _queueIndex = newPos;
    _skipState = offset > 0
        ? AudioProcessingState.skippingToNext
        : AudioProcessingState.skippingToPrevious;
    AudioServiceBackground.setMediaItem(mediaItem);
    await _audioPlayer.setUrl(mediaItem.id);
    print(mediaItem.id);
    _skipState = null;
    if (_playing) {
      onPlay();
    } else {
      _setState(processingState: AudioProcessingState.ready);
    }
  }

  @override
  Future<void> onStop() async {
    _playing = false;
    await _audioPlayer.stop();
    await _audioPlayer.dispose();
    _playerStateSubscription.cancel();
    _eventSubscription.cancel();
    return await super.onStop();
  }

  @override
  void onSeekTo(Duration position) {
    _audioPlayer.seek(position);
  }

  @override
  void onClick(MediaButton button) {
    playPause();
  }

  @override
  Future<void> onFastForward() async {
    await _seekRelative(fastForwardInterval);
  }

  @override
  Future<void> onRewind() async {
    await _seekRelative(rewindInterval);
  }

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

  _handlePlaybackCompleted() {
    if (hasNext) {
      onSkipToNext();
    } else {
      onStop();
    }
  }

  void playPause() {
    if (AudioServiceBackground.state.playing)
      onPause();
    else
      onPlay();
  }

  Future<void> _setState({
    AudioProcessingState processingState,
    Duration position,
    Duration bufferedPosition,
  }) async {
    print('SetState $processingState');
    if (position == null) {
      position = _audioPlayer.playbackEvent.position;
    }
    await AudioServiceBackground.setState(
      controls: getControls(),
      systemActions: [MediaAction.seekTo],
      processingState:
      processingState ?? AudioServiceBackground.state.processingState,
      playing: _playing,
      position: position,
      bufferedPosition: bufferedPosition ?? position,
      speed: _audioPlayer.speed,
    );
  }

  List<MediaControl> getControls() {
    if (_playing) {
      return [
        skipToPreviousControl,
        pauseControl,
        stopControl,
        skipToNextControl
      ];
    } else {
      return [
        skipToPreviousControl,
        playControl,
        stopControl,
        skipToNextControl
      ];
    }
  } this is my class
}

class AudioState {
  final List<MediaItem> queue;
  final MediaItem mediaItem;
  final PlaybackState playbackState;

  AudioState(this.queue, this.mediaItem, this.playbackState);
}

Answer 1

您应该覆盖this method inAudioPlayerTask` 类：

  @override
  // ignore: missing_return
  Future<Function> onAddQueueItem(MediaItem mediaItem) async{
    // queue.add(mediaItem); or somthing like this to update your queue
    await AudioServiceBackground.setQueue(queue);
    try {
      await _player.load(ConcatenatingAudioSource(
        children:
        queue.map((item) => AudioSource.uri(Uri.parse(item.id))).toList(),
      ));
      // In this example, we automatically start playing on start.
      onPlay();
    } catch (e) {
      print("Error: $e");
      onStop();
    }
  }

然后你可以在你的 UI 中调用这个函数：

await AudioService.start(
                        backgroundTaskEntrypoint: audioPlayerTaskEntrypoint,
                        androidNotificationChannelName:
                            'Audio Service Demo',
                        // Enable this if you want the Android service to exit the foreground state on pause.
                        //androidStopForegroundOnPause: true,
                        androidNotificationColor: 0xFF2196f3,
                        androidNotificationIcon: 'mipmap/ic_launcher',
                        androidEnableQueue: true,
                      );
// call this func:
await AudioService.addQueueItem(m);

Answer 2

根据作者 here 的说法，该插件最初不允许直接将任何参数传递给后台任务。它旨在让后台任务通过 SQLite 或 null 等工具在内部查询要从内部存储播放的内容。

但是今天，该插件允许通过我确定的 3 种不同方式将媒体数据传递给后台任务：

shared_preferences 与 above answer 以及 this one 中提到的 AudioService.addQueueItem(item) 结合
onAddQueueItem 结合 AudioService.customAction('url', url) 解释here
使用 onCustomAction 方法的 Map<String, dynamic> params 参数。它作为后台任务的 AudioService.start 方法的参数接收，如here

在颤振中，我们如何使用audio_service来获取动态数据

2 个答案: