Flutter BLoC State Management

BLoC State Management

Priority: P0 (CRITICAL)

Predictable state management separating business logic from UI using bloc, freezed, or equatable.

Structure

presentation/​blocs/
├── auth/
│   ├── auth_bloc.dart
│   ├── auth_event.dart # (@freezed or Equatable)
│   └── auth_state.dart # (@freezed or Equatable)

Implementation Guidelines

• States & Events: Default to @freezed (Priority). Use Equatable if the library is present in pubspec.yaml.
  • freezed: Use for union states (initial, loading, success) and automatic copyWith.
  • Equatable: Apply if code generation (build_runner) is avoided or equatable is the only comparison library in pubspec.yaml.
  • Choose strategy:
    • Union State: Exclusive UI phases (loading vs data).
    • Property-based State: Complex forms (Option<$Either>, flags).
• State Properties: Use enums, sealed classes, or Status objects.
• Error Handling: Use Failure objects; avoid throwing exceptions.
• Async Data: Use emit.forEach or emit.onEach for streams.
• Concurrency: Use transformer (restartable, droppable) for event debouncing.
• Testing: Use blocTest for state transition verification.
• Injection: Register BLoCs as @injectable (Factory).

Anti-Patterns

• No Manual Emit: Do not call emit() inside Future.then; always use await or emit.forEach.
• No UI Logic: Do not perform calculations or data formatting inside BlocBuilder.
• No Cross-Bloc Reference: Do not pass a BLoC instance into another BLoC; use streams or the UI layer to coordinate.

Reference & Examples

For full BLoC/​Cubit implementations and concurrency patterns: See references/​REFERENCE.md.

Related Topics

feature-based-clean-architecture | dependency-injection