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avoid-passing-bloc-to-bloc

added in: 1.2.0
warning
Pro+

Warns when a Bloc depends on another Bloc.

Because blocs expose streams, it may be tempting to make a bloc which listens to another bloc. You should not do this. A bloc should only receive information through events and from injected repositories (i.e., repositories given to the bloc in its constructor).

If you're in a situation where a bloc needs to respond to another bloc, you can push the problem up a layer (into the presentation layer), or down a layer (into the domain layer).

Example​

❌ Bad:

class BadBloc extends Bloc<CounterEvent, int> {
  final OtherBloc otherBloc;
  late final StreamSubscription otherBlocSubscription;

  // LINT: Avoid creating a dependency between two 'Blocs'.
  BadBloc(this.otherBloc) : super(0) {
    otherBlocSubscription = otherBloc.stream.listen((state) {
      add(Change(1));
    });
  }

  @override
  void onChange(Change<int> change) {
    super.onChange(change);
    ...
  }
}

class OtherBloc extends Bloc<CounterEvent, int> {
  OtherBloc() : super(0);

  @override
  void onChange(Change<int> change) {
    super.onChange(change);
    ...
  }
}

✅ Good:

class GoodBloc extends Bloc<CounterEvent, int> {
  // You can pass the stream instead
  GoodBloc() : super(0) { }

  @override
  void onChange(Change<int> change) {
    super.onChange(change);
    ...
  }
}

Additional Resources​