CODEWITHSUNDEEP
dartflutterstreamiteration
Francesco Iapicca
Francesco Iapicca

Reputation: 2657

Dart / Flutter: Error "Stream has already been listened to." && "await for" inside fa "for loop" fails

aye aye good people,

I'm probably missing something here:

this code is fictional (it's an oversimplification, for everyone convenience), but gives the idea:

_map.keys.forEach((key) async {
   _bloc.sink.add(_map[key]);
await for (String _string in _bloc.stream) {
  _newMap.putIfAbsent(key, ()=> _string);
 }
});

or 

Stream.fromIterable(_map.keys).forEach((day) async {
    _bloc.sink.add(_map[key]);
await for (String _string in _bloc.stream) {
  _newMap.putIfAbsent(key, ()=> _string);
 }
});

with StreamController<...>.broadcast(); the streams seams healthly:

first:_Future hashCode:817453996 isBroadcast:true isEmpty:_Future last:_Future length:_Future runtimeType:Type (_BroadcastStream<...>) single:_Future _awaiter:null _generator:null _controller:_AsyncBroadcastStreamController

without returns this error:

first:Unhandled exception:\nBad state: Stream has already been listened to.[...] hashCode:644468606 isBroadcast:false isEmpty:Unhandled exception:\nBad state: Stream has already been listened to.[...] last:Unhandled exception:\nBad state: Stream has already been listened to.[...] length:Unhandled exception:\nBad state: Stream has already been listened to.[...] runtimeType:Type (_ControllerStream<...>) single:Unhandled exception:\nBad state: Stream has already been listened to.[...] _awaiter:null _generator:null _controller:_AsyncStreamController

in both cases, doesn't work.

what I intended to do is (inside a for loop) to send in the sink a collection,

a bloc will do some work and return another collection in the stream,

what I can see from debug is that the loop just keep sending stuff to the sink.

I'm not sure that is because:

...

1) the loop doesn't wait for "await for"

and causes the error "stream already listen"

2) vice-versa the "await for " cannot listen to the stream because of the error

(or because the broadcast can lose the event) therefore the loop keep looping(?);

...

I'm more incline to about the first one, but it should work according to this POST

what am I doing wrong?

thank you in advance, Francesco

Upvotes: 0

Views: 1019

Answers (1)

Gugo Hovhannisyan
Gugo Hovhannisyan

Reputation: 344

This seems like you calling stream.listen more than once. Try to assign the _bloc.stream to a variable outside of your for loop.

var stream = _bloc.stream;


_map.keys.forEach((key) async {
  _bloc.sink.add(_map[key]);
await for (String _string in stream) {
 _newMap.putIfAbsent(key, ()=> _string);
}
});

Upvotes: 1

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