Flutter：尝试两次收听广播流时出现异常

Question

我有一个包含广播流的存储

 Stream<List<DeliveryModel>> get deliveriesStream {
    this._getDeliveries();
    return this._controller.stream.asBroadcastStream();
  }

并且有两个订阅者，一旦我开始手动收听，

var stream = this._deliveryRepo.deliveriesStream;
    deliveriesSubscription = stream.listen((deliveries) {
    // to do something 
});

并通过 StreamBuilder

一次

@override
  void initState() {
    super.initState();
    this.stream = this.widget.deliveriesFetcher.getDeliveriesStream();
  }

  @override
  Widget build(BuildContext context) {
    return StreamBuilder(
        stream: this.stream,
        builder: (context, snapshot) {
          // do something
        });
  }

其中

@override
  Stream<List<DeliveryModel>> getDeliveriesStream() {
    return this._deliveryRepo.deliveriesStream;
  }

如果我没理解错的话，我订阅了两次广播流，所以一切都应该没问题，但是当我第二次尝试订阅流时（通过 StreamBuilder），它会抛出异常：错误状态：流已被收听。有什么建议吗？

Answer 1

原因是每次 deliveriesStream getter 调用时您都在创建一个新的 BroadcastStream。尝试使用这样的东西：

Stream<List<DeliveryModel>> _deliveriesStream;

Stream<List<DeliveryModel>> get deliveriesStream {
  this._getDeliveries();
  _deliveriesStream ??= _controller.stream.asBroadcastStream();
  return _deliveriesStream;
}

Flutter：尝试两次收听广播流时出现异常

Flutter: Exception while trying to listen to Broadcast stream twice

dart-async

flutter