dart - StreamBuilder 没有在流中的新事件上重建

Question

我的 StreamBuilder 在 View 中:

Widget build(BuildContext context) {
    print("rebuilding..."); // as of now this gets called only on view initialization and never again - i.e. not on new events going through alarmController.stream

    return StreamBuilder(
        stream: widget.bloc.alarmController.stream,
        initialData: Alarm(''),
        builder: (BuildContext context, AsyncSnapshot<Alarm> snapshot) {
          if (!snapshot.hasData) {
            return Center(
              child: Text(StringLiterals.NO_ALARM_DATA_MSG))
            );
          }

          return Switch(
                  activeColor: Colors.red,
                  value: snapshot.data.status == 'Started',
                  onChanged: (bool _value) {
                    _newAlarmValue = _value;
                    _askAlarmConfirmation();
                  }));
        });
  }

我 Bloc 的核心:

AlarmBloc(this.Api) {
    getAlarm();
}
  getAlarm() async {
    Alarm response = await Api.getAlarmStatus();
    alarmController.sink.add(response); // here im adding new event, therefore streambuilder should rebuild, right?
}

最后是我调用来启动新事件的代码(在本例中是 firebase 消息):

if(_message.notification.body.contains("Alarm") && IS_LOGGED_IN == true) {
   alarmBloc.getAlarm();
 }

所以问题是 StreamBuilder 不会在新事件通过 alarmController.stream 时重建。可能是什么原因？

Answer 1

您的 bloc 需要是一种 Stream。与您的 StreamBuilder 相同的流类型。例如，您的 Bloc 需要是 Stream<Alarm> .否则stream: widget.bloc.alarmController.stream,只会被调用一次，不会充当异步数据流。

您的 Streambuilder 需要检查连接状态

Widget build(BuildContext context) {
    print("rebuilding..."); // as of now this gets called only on view initialization and never again - i.e. not on new events going through alarmController.stream

    return StreamBuilder<Alarm>(
        stream: widget.bloc.alarmController.stream,
        initialData: Alarm(''),
        builder: (BuildContext context, AsyncSnapshot<Alarm> snapshot) {
          if (snapshot.hasError) return new Text('Error: ${snapshot.error}');
      switch (snapshot.connectionState) {
        case ConnectionState.waiting:
          return Text('Loading...'); 
        default: 
          if (!snapshot.hasData) {
             return Center(
                child: Text(StringLiterals.NO_ALARM_DATA_MSG))
             );
          }

         return Switch(
              activeColor: Colors.red,
              value: snapshot.data.status == 'Started',
              onChanged: (bool _value) {
                _newAlarmValue = _value;
                _askAlarmConfirmation();
              }));
      }

以下是您可以检查的其他类型的连接状态:

async.dart

    enum ConnectionState {
  /// Not currently connected to any asynchronous computation.
  ///
  /// For example, a [FutureBuilder] whose [FutureBuilder.future] is null.
  none,

  /// Connected to an asynchronous computation and awaiting interaction.
  waiting,

  /// Connected to an active asynchronous computation.
  ///
  /// For example, a [Stream] that has returned at least one value, but is not
  /// yet done.
  active,

  /// Connected to a terminated asynchronous computation.
  done,
}