Flutter BLoC Project Structure

BLoC pattern with flutter_bloc. Event-driven state management with clear separation of concerns.

#flutter #dart #mobile #bloc #state-management

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Project Directory

myapp/

pubspec.yaml

pubspec.lock

analysis_options.yaml

.gitignore

lib/

main.dart

MultiBlocProvider setup

app.dart

core/

constants/

theme/

blocs/

App-wide blocs

app_bloc_observer.dart

Debug observer

features/

auth/

bloc/

Feature BLoC

auth_bloc.dart

auth_event.dart

auth_state.dart

data/

auth_repository.dart

user_model.dart

screens/

login_screen.dart

widgets/

home/

bloc/

data/

screens/

widgets/

shared/

widgets/

models/

routing/

app_router.dart

test/

features/

auth/

bloc/

bloc_test tests

android/

ios/

assets/

Why This Structure?

BLoC (Business Logic Component) enforces strict separation between UI and logic. Events go in, states come out. Highly testable with bloc_test package. Predictable state changes through the event-driven pattern.

Key Directories

lib/features/*/bloc/-BLoC, events, and states per feature
*_bloc.dart-Handles events, emits states
*_event.dart-User actions as sealed classes
*_state.dart-UI states as sealed classes

BLoC Event Handler

// lib/features/auth/bloc/auth_bloc.dart
class AuthBloc extends Bloc {
  final AuthRepository _authRepository;

  AuthBloc(this._authRepository) : super(AuthInitial()) {
    on(_onLoginRequested);
  }

  Future _onLoginRequested(
    LoginRequested event, Emitter emit
  ) async {
    emit(AuthLoading());
    try {
      final user = await _authRepository.login(event.email, event.password);
      emit(AuthSuccess(user));
    } catch (e) {
      emit(AuthFailure(e.toString()));
    }
  }
}

Getting Started

flutter pub add flutter_bloc equatable
flutter pub add -d bloc_test
Create feature with bloc/, screens/, widgets/
Provide BLoC via BlocProvider
Consume with BlocBuilder/BlocConsumer

When To Use This

Need strict separation of concerns
Want excellent testability with bloc_test
Team prefers explicit event-driven architecture
Complex UI state transitions
Large apps with many state changes

Trade-offs

Boilerplate-Event, state, and bloc files per feature
Learning curve-Streams and event-driven thinking required
Verbosity-More code than simpler solutions