Flutter Riverpod：使用 StreamProvider 返回 2 个流

问题描述

我有使用包 Asset Audio Player 和 Flutter Riverpod 作为状态管理的音乐播放器应用程序。我想听两件事：

收听当前歌曲的时长
收听当前播放的歌曲

final currentSongPosition = StreamProvider.autodispose<Map<String,dynamic>>((ref) async* {
  final AssetsAudioPlayer player = ref.watch(globalAudioPlayers).state;
  ref.ondispose(() => player.dispose());

  final Stream<double> _first = player.currentPosition.map((event) => event.inSeconds.todouble());
  final Stream<double> _second =
      player.current.map((event) => event?.audio.duration.inSeconds.todouble() ?? 0.0);

  final maps = {};
  maps['currentDuration'] = _first;
  maps['maxDurationSong'] = _second;
  return maps; << Error The return type 'Map<dynamic,dynamic>' isn't a 'Stream<Map<String,dynamic>>',as required by the closure's context.
});

如何将 2 个流返回到 1 个 StreamProvider 然后我可以简单地使用：

Consumer(
              builder: (_,watch,__) {
               
                final _currentSong = watch(currentSongPosition);

                return _currentSong.when(
                  data: (value) {
                    final _currentDuration = value['currentDuration'] as double;
                    final _maxDuration = value['maxDuration'] as double;
                    return Text('Current : $_currentDuration,Max :$_maxDuration');
                  },loading: () => Center(child: CircularProgressIndicator()),error: (error,stackTrace) => Text('Error When Playing Song'),);
               
              },),

解决方法

我首先为每个 StreamProvider 创建一个 Stream：

final currentDuration = StreamProvider.autoDispose<double>((ref) {
  final player = ref.watch(globalAudioPlayers).state;
  return player.currentPosition.map((event) => event.inSeconds.toDouble());
});

final maxDuration = StreamProvider.autoDispose<double>((ref) {
  final player = ref.watch(globalAudioPlayers).state;
  return player.current.map((event) => event?.audio.duration.inSeconds.toDouble() ?? 0.0);
});

接下来，创建一个 FutureProvider 以读取每个 Stream 的最后一个值。

final durationInfo = FutureProvider.autoDispose<Map<String,double>>((ref) async {
  final current = await ref.watch(currentDuration.last);
  final max = await ref.watch(maxDuration.last);
  return {
    'currentDuration': current,'maxDurationSong': max,};
});

最后，创建一个将 StreamProvider 转换为 durationInfo 的 Stream。

final currentSongPosition = StreamProvider.autoDispose<Map<String,double>>((ref) {
  final info = ref.watch(durationInfo.future);
  return info.asStream();
});

这个答案是@AlexHartford 所做的另一种方法。

我的案例当前的解决方案是使用包 rxdart CombineLatestStream.list()，然后应该查看此代码：

流提供者

final currentSongPosition = StreamProvider.autoDispose((ref) {
  final AssetsAudioPlayer player = ref.watch(globalAudioPlayers).state;

  final Stream<double> _first = player.currentPosition.map((event) => event.inSeconds.toDouble());
  final Stream<double> _second =
      player.current.map((event) => event?.audio.duration.inSeconds.toDouble() ?? 0.0);

  final tempList = [_first,_second];
  return CombineLatestStream.list(tempList);
});

如何使用：

Consumer(
              builder: (_,watch,__) {
                final players = watch(globalAudioPlayers).state;
                final _currentSong = watch(currentSongPosition);
                return _currentSong.when(
                  data: (value) {
                    final _currentDuration = value[0];
                    final _maxDuration = value[1];
                    return Slider.adaptive(
                      value: _currentDuration,max: _maxDuration,onChanged: (value) async {
                        final newDuration = Duration(seconds: value.toInt());
                        await players.seek(newDuration);
                        context.read(currentSongProvider).setDuration(newDuration);
                      },);
                  },loading: () => const Center(child: CircularProgressIndicator()),error: (error,stackTrace) => Text(error.toString()),);
              },),

但是这种方法有一个缺点，代码难以阅读。特别是在Consumer中使用时，我必须知道返回结果的顺序。

dart riverpod