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我正在尝试在我的 Player 类上提供我的 audioHandler，但是发生了一些奇怪的事情

当我进入屏幕时，StreamBuilder 会很好地激活，但如果我再次弹出并导航到屏幕，流连接将永远保持“等待”状态，除非我播放音频。这会导致一些奇怪的行为。我做错了什么？

相关代码

玩家等级

final audioHandlerProvider = Provider<AudioHandler>((ref) {
  AudioHandler _audioHandler = ref.read(audioHandlerServiceProvider);

  return _audioHandler;
});

class _PlayerClicVozzState extends State<PlayerClicVozz> {
  @override
  Widget build(BuildContext context) {

    return Scaffold(
      extendBodyBehindAppBar: true,
      backgroundColor: Color(0xff131313),
      appBar: AppBar(
        automaticallyImplyLeading: false,
        actions: [
          IconButton(
            icon: Icon(Icons.clear, color: Colors.white),
            onPressed: () => Navigator.of(context).pop(),
          ),
        ],
        backgroundColor: Colors.transparent,
        elevation: 0,
      ),
      body: Center(
        child: Consumer(builder: (context, watch, child) {
          final res = watch(audioHandlerProvider);
          return StreamBuilder<MediaState>(
            stream: _mediaStateStream(res),
            builder: (context, snapshot) {
              final mediaState = snapshot.data;
              return SeekBar(
                duration: mediaState?.mediaItem?.duration ?? Duration.zero,
                position: mediaState?.position ?? Duration.zero,
                onChangeEnd: (newPosition) {
                  res.seek(newPosition);
                },
              );
            },
          );
...

音频服务初始化

late AudioHandler _audioHandler;

final audioHandlerServiceProvider = Provider<AudioHandler>((ref) {
  return _audioHandler;
});

Future<void> main() async {
  _audioHandler = await AudioService.init(
    builder: () => AudioPlayerHandler(),
    config: AudioServiceConfig(
      androidNotificationChannelId: 'com.mycompany.myapp.channel.audio',
      androidNotificationChannelName: 'Audio playback',
      androidNotificationOngoing: true,
    ),
  );
...

我的音频处理程序与插件示例完全相同


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

class AudioPlayerHandler extends BaseAudioHandler with SeekHandler {
  static final _item = MediaItem(
    id: 'https://s3.amazonaws.com/scifri-episodes/scifri20181123-episode.mp3',
    album: "Science Friday",
    title: "A Salute To Head-Scratching Science",
    artist: "Science Friday and WNYC Studios",
    duration: const Duration(milliseconds: 5739820),
    artUri: Uri.parse(
        'https://media.wnyc.org/i/1400/1400/l/80/1/ScienceFriday_WNYCStudios_1400.jpg'),
  );

  final _player = AudioPlayer();

  /// Initialise our audio handler.
  AudioPlayerHandler() {
    // So that our clients (the Flutter UI and the system notification) know
    // what state to display, here we set up our audio handler to broadcast all
    // playback state changes as they happen via playbackState...
    _player.playbackEventStream.map(_transformEvent).pipe(playbackState);
    // ... and also the current media item via mediaItem.
    mediaItem.add(_item);

    // Load the player.
    _player.setAudioSource(AudioSource.uri(Uri.parse(_item.id)));
  }

  // In this simple example, we handle only 4 actions: play, pause, seek and
  // stop. Any button press from the Flutter UI, notification, lock screen or
  // headset will be routed through to these 4 methods so that you can handle
  // your audio playback logic in one place.

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

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

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

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

  /// Transform a just_audio event into an audio_service state.
  ///
  /// This method is used from the constructor. Every event received from the
  /// just_audio player will be transformed into an audio_service state so that
  /// it can be broadcast to audio_service clients.
  PlaybackState _transformEvent(PlaybackEvent event) {
    return PlaybackState(
      controls: [
        MediaControl.rewind,
        if (_player.playing) MediaControl.pause else MediaControl.play,
        MediaControl.stop,
        MediaControl.fastForward,
      ],
      systemActions: const {
        MediaAction.seek,
        MediaAction.seekForward,
        MediaAction.seekBackward,
      },
      androidCompactActionIndices: const [0, 1, 3],
      processingState: const {
        ProcessingState.idle: AudioProcessingState.idle,
        ProcessingState.loading: AudioProcessingState.loading,
        ProcessingState.buffering: AudioProcessingState.buffering,
        ProcessingState.ready: AudioProcessingState.ready,
        ProcessingState.completed: AudioProcessingState.completed,
      }[_player.processingState]!,
      playing: _player.playing,
      updatePosition: _player.position,
      bufferedPosition: _player.bufferedPosition,
      speed: _player.speed,
      queueIndex: event.currentIndex,
    );
  }
}

MediaStateStream 和 QueueStateStream

  Stream<MediaState> _mediaStateStream(AudioHandler audioHandler) {
    return Rx.combineLatest2<MediaItem?, Duration, MediaState>(
        audioHandler.mediaItem,
        AudioService.position,
        (mediaItem, position) => MediaState(mediaItem, position));
  }

  _queueStateStream(AudioHandler audioHandler) {
    return Rx.combineLatest2<List<MediaItem>?, MediaItem?, QueueState>(
        audioHandler.queue,
        audioHandler.mediaItem,
        (queue, mediaItem) => QueueState(queue, mediaItem));
  }
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1 回答 1

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当您订阅一个流时，您只会开始接收在您订阅之后发出的新事件，并且您可能需要一段时间等待下一个事件。

在您的实现中，_mediaStateStream您正在使用AudioService.positionwhich 仅在位置变化时发出事件（即未暂停或停止）。因此，即使流过去可能已经发出位置事件，如果您在暂停或停止时再次订阅该流，您将处于等待状态，直到下一个位置事件到达，即在再次恢复播放之后。

我建议将您的流包装在 rxdart 中BeehaviorSubject，以便它保留最后一个事件的内存并将最后一个事件重新发送给新的听众。此外，您可以BehaviorSubject使用第一个值作为种子，以确保即使是第一个侦听器也没有等待期：

_mediaStateSubject = BehaviorSubject.seeded(MediaState(
    handler.mediaItem.valueOrNull,
    handler.playbackState.position))
  ..addStream(_mediaStateStream(handler));

然后你可以听_mediaStateSubject而不是_mediaStateStream。

于 2021-11-22T08:39:02.037 回答