flutter - 相同的StreamBuilders处于波动状态，一个正在工作而其他返回null

Question

我在两个不同的小部件中有两个相同的流生成器​​。一个有效，而另一个不接收任何数据。这是小部件树。

这是StreamBuilder

StreamBuilder<AudioPlayerState>(
    stream: _playbackProvider.playbackState,
    builder: (context, snapshot) {
      IconData _playbackButton = Icons.play_circle_filled;

         if (snapshot.hasData) {
             if (snapshot.data == AudioPlayerState.PLAYING) {
                  _playbackButton = Icons.pause_circle_filled;
             } else {
                  _playbackButton = Icons.play_circle_filled;
             }
         }

        return OutlineButton(
             onPressed: () {
               _playButtonClicked(snapshot.data);
             },
             child: Icon(_playbackButton),
             shape: CircleBorder(),
        );
}),

这是他们俩都在听的流:

Stream<AudioPlayerState> get playbackState {
    return _audioPlayer.onPlayerStateChanged; // using onPlayerStateChanged stream provided by audioplayers plugin.
}

变更通知程序提供者可以在这两个小部件(脚手架)中访问此流。音频播放器包含在ChangeNotifier类中。

class PlaybackProvider with ChangeNotifier {
  String _path;
  AudioPlayer _audioPlayer;

  PlaybackProvider() {
    _audioPlayer = AudioPlayer();
    _audioPlayer.setReleaseMode(ReleaseMode.STOP);
    _audioPlayer.notificationState = AudioPlayerState.STOPPED;
  }

  Stream<Duration> get playbackPosition { // this stream is also working fine in the first screen (widget)
    return _audioPlayer.onAudioPositionChanged;
  }

  Stream<AudioPlayerState> get playbackState {
    return _audioPlayer.onPlayerStateChanged;
  }

//other methods
}

然后将更改通知程序提供给这些小部件中的每个。

final _playbackProvider = Provider.of<PlaybackProvider>(context);

还有主要功能

void main() {
  runApp(MultiProvider(providers: [
    ChangeNotifierProvider(create: (_) => PlaylistProvider()),
    ChangeNotifierProvider(create: (_) => PlaybackProvider()),
  ], child: MyApp()));
}

Answer 1

Stream<Duration> get playbackPosition { // this stream is also working fine in the first screen (widget)
    return _audioPlayer.onAudioPositionChanged;
  }

您确定_audioPlayer.onAudioPositionChanged是BroadcastStream还是返回了Strem的相同实例，可能是getter每次调用时都返回不同的实例的一种情况，一种确保您具有相同值的方法是创建StreamProvider，然后将其消耗到树中

void main() {
  runApp(MultiProvider(providers: [
    ChangeNotifierProvider(create: (_) => PlaylistProvider()),
    ChangeNotifierProvider(create: (_) => PlaybackProvider()),
    StreamProvider<AudioPlayerState>(create: (context) => Provider.of<PlaybackProvider>(context, listen: false).playbackState)
  ], child: MyApp()));
}

然后，使用每个使用者代替每个小部件中的StreamBuilder

return OutlineButton(
  onPressed: () => _playButtonClicked(snapshot.data),
  child: Consumer<AudioPlayerState>(
    builder: (context, data, _) {
      if(data  == AudioPlayerState.PLAYING) return Icon(Icons.pause_circle_filled);
      return Icon(Icons.play_circle_filled);
    }
  ),
  shape: CircleBorder(),
);

您的代码和逻辑没有错，但是如果您使用提供程序，则最好(单反)使用它提供的所有类型的提供程序都对您有利。如果您想继续使用StreamBuilder，那也很好，但是如果看不到AudioPlayer类的代码，则很难确定返回的_audioPlayer.onAudioPositionChanged的内容，如果它是简单的流，是否要在该方法中重新创建它，即Broadcast(使用asBroadCast方法)等？