feat(bloc)!: expose Emitter in Cubit

[felangel]

Status

IN DEVELOPMENT

Breaking Changes

YES

Description

• feat(bloc)!: expose Emitter in Cubit
  • support emit.forEach and emit.onEach in Cubit
• refactor(bloc)!: decouple BlocBase implementation from interface (closes #refactor(bloc): Extract base bloc interface #2453)

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore

[codecov]

Codecov Report

Merging #2896 (44a86b4) into feat/v8.0.0 (71c332f) will not change coverage.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           feat/v8.0.0     #2896    +/-   ##
==============================================
  Coverage       100.00%   100.00%            
==============================================
  Files               25         6    -19     
  Lines              639       261   -378     
==============================================
- Hits               639       261   -378     

Impacted Files	Coverage Δ
packages/bloc/lib/src/bloc.dart	100.00% <100.00%> (ø)
packages/flutter_bloc/lib/src/bloc_selector.dart
packages/bloc_concurrency/lib/src/concurrent.dart
packages/bloc_test/lib/src/mock_bloc.dart
...ages/flutter_bloc/lib/src/repository_provider.dart
packages/hydrated_bloc/lib/src/hydrated_bloc.dart
packages/flutter_bloc/lib/src/bloc_listener.dart
...ackages/hydrated_bloc/lib/src/hydrated_cipher.dart
packages/flutter_bloc/lib/src/bloc_provider.dart
... and 11 more

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[felangel]

@jeroen-meijer @definitelyokay after thinking about it I'd prefer not to support the Emitter API for Cubit for several reasons:

• emit.forEach and emit.onEach while functional in Cubit will not be cancelable which imo reduces the usefulness significantly
• The new API opens the door to developers being able to cache a reference of an Emitter since emit would be a getter
• isDone only makes sense in the context of Bloc but is part of the base Emitter interface so we'd either need to have a specific BlocEmitter and CubitEmitter or Cubit users would have access to a useless property.

Would love to hear what you all think, thanks!

[jolexxa]

• The new API opens the door to developers being able to cache a reference of an Emitter since emit would be a getter
• isDone only makes sense in the context of Bloc but is part of the base Emitter interface so we'd either need to have a specific BlocEmitter and CubitEmitter or Cubit users would have access to a useless property.

You're absolutely right. It was a nice idea, but I guess it's bad in practice. Didn't foresee that, but live and learn 🤷‍♀️

[marctan]

Hello, sorry for bumping this thread., but if I want to listen to a stream in Cubit class is below correct?

class ChatCubit extends Cubit<ChatState> {
  ChatCubit({required this.repository}) : super(const ChatState());
  final ChatRepository repository;
 StreamSubscription? subscription;

  @override
  Future<void> close() {
    subscription?.cancel();
    return super.close();
  }

void getMessages(String recipient) async {
    emit(state.copyWith(status: ChatStatus.messagesLoading));
    await subscription?.cancel();

    subscription = repository.getMessageStream(recipient).listen((event) {
      final List<ChatMessage> messageList = event.docs
          .map(
            (e) => ChatMessage(
              text: e['message'],
              user: ChatUser(
                uid: e['sender'],
                name: e['sender'],
              ),
              createdAt: DateTime.fromMillisecondsSinceEpoch(
                e['time'],
              ),
            ),
          )
          .toList();
      emit(state.copWith(status: ChatStatus.messagesLoaded, messages: messageList));
    });
  }
}

Thanks!
@felangel

[Gene-Dana]

Feel free to put the subscription in the constructor body too!

[zamaniafshar]

• emit.forEach and emit.onEach while functional in Cubit will not be cancelable which imo reduces the usefulness significantly
• The new API opens the door to developers being able to cache a reference of an Emitter since emit would be a getter
• isDone only makes sense in the context of Bloc but is part of the base Emitter interface so we'd either need to have a specific BlocEmitter and CubitEmitter or Cubit users would have access to a useless property.

I think the main reason this hasn’t been done yet is due to implementation challenges, not because adding these features to Cubit is a bad idea.
I really hope this feature is added to Bloc soon, as it’s a big pain to have to use Bloc in many situations just because of a few streams—which feels unreasonable. In the meantime, I've created a solution for myself.
#3555 (comment)