If you use BLoC as your approach to state management in Flutter, there is a good chance you also depend on the bloc and flutter_bloc packages to reduce boilerplate. With version 5, bloc received a major update. Let’s look at what changed.

Hello cubit!

The most important change in this release is that both bloc and flutter_bloc now build on top of cubit, a new lightweight state-management package created by Felix Angelov.

Unlike classic bloc, cubit removes the Event layer and updates state directly through methods. You can think of it as a smaller, simpler state-management core. My impression is that this split made the internals easier to evolve and also lowered the barrier for developers who were hesitant to adopt bloc because of its event-driven model.

Goodbye initialState

In bloc v5, the old initialState getter is gone. Instead, you now provide the initial state through the superclass constructor.

    class SomeBloc extends Bloc<SomeEvent, SomeState> {
      SomeBloc() : super(InitialState());

      @override
      Stream<int> mapEventToState(SomeEvent event) async* {

      }
    }

As a result, the initialState getter that used to come with every Bloc subclass disappears as well.

No more BlocSupervisor

BlocSupervisor, which many people used to install a BlocDelegate for logging states and events, is no longer part of the API. At the same time, BlocDelegate was renamed to BlocObserver, which is a clearer name for what the type actually does.

The new usage is also more direct:

    class SomeBlocObserver extends BlocObserver {
      @override
      void onTransition(Bloc bloc, Transition transition) {
        print(transition);
        super.onTransition(bloc, transition);
      }
    }

    void main() {
    	// ...
        Bloc.observer = SomeBlocObserver();
        // ...
    }

flutter_bloc

On the flutter_bloc side, some properties were renamed to make their intent clearer:

condition in BlocBuilder became buildWhen

condition in BlocListener became listenWhen

Beyond that, the release also included general bug fixes and a refreshed logo. If you want the full details, check the official changelogs for bloc and flutter_bloc.

Thanks for reading

📚 Hope you enjoy reading!