How can Bloc listen to stream and emit state

Issue

In my flutter app, I use flutter_bloc for state management.

The bloc in question uses a repository. The repository subscribes to a websocket, and new data is added to a stream.

Problem:
My bloc listens to the stream:

InvestmentClubBloc({
    required this.investmentClubRepository
  }) : super(InvestmentClubLoading()) {
    onChangeSubscription = investmentClubRepository.onNewMessage.listen(
      (event) {
        emit(NewMessageState(event); // <-- The member "emit" can only be used within 'package:bloc/src/bloc.dart' or in test
      },
    );
  }

The problem is that emit does not work (I get the warning "The member "emit" can only be used within ‘package:bloc/src/bloc.dart’ or in test")

How can bloc listen to a stream and emit new states depending on stream events?

Solution

You should use emit in eventHandler, use below code to complete your task:

abstract class Event {}

class DemoEvent extends Event {}

var fakeStream =
    Stream<int>.periodic(const Duration(seconds: 1), (x) => x).take(15);

class DemoBloc extends Bloc<Event, int> {
  DemoBloc() : super(0) {
    fakeStream.listen((_) {
      // add your event here
      add(DemoEvent());
    });
    on<DemoEvent>((_, emit) {
      // emit new state
      emit(state + 1);
    });
  }
}

Answered By – 聂超群

Answer Checked By – David Goodson (FlutterFixes Volunteer)

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