Flutter Bloc

BLoC Pattern

• Sealed States & Events: Always use sealed class for both States and Events to ensure exhaustive UI handling and compile-time safety.
• Immutability: All States, Events, and Domain Entities MUST be immutable (using final and Equatable or freezed).
• Official BLoC Part-Part Of Pattern: Every _bloc.dart file MUST include its corresponding _event.dart and _state.dart files using part directives. Each event/state file MUST have a part of directive pointing back to the bloc file. This ensures a single library scope and shared private members.

  // auth_bloc.dart
  part 'auth_event.dart';
  part 'auth_state.dart';
  
  class AuthBloc extends Bloc<AuthEvent, AuthState> { ... }
  
  // auth_event.dart
  part of 'auth_bloc.dart';
  
  // auth_state.dart
  part of 'auth_bloc.dart';
  

• Mandatory Directory Structure: Every BLoC feature set MUST reside in its own sub-directory within the bloc/ folder. Flat bloc/ directories are STRICTLY prohibited.

  presentation/bloc/
  └── <bloc_name>/
      ├── <bloc_name>_bloc.dart
      ├── <bloc_name>_event.dart
      └── <bloc_name>_state.dart
  

• Loading State Mandate: ALWAYS emit Loading before async work, then Success or Error. Never skip the loading state.
• Concurrency: Use transformers (e.g., restartable(), droppable()) for events requiring debouncing (search) or throttling (buttons).
• Zero-Logic UI: Widgets MUST NOT contain business logic, orchestration logic, or direct calls to external services. They should ONLY dispatch events and build UI based on BLoC states.

BLoC Widget Usage

• BlocBuilder for local UI rebuilds based on state
• BlocListener for side effects (navigation, snackbars, dialogs)
• BlocConsumer when both rebuild and side effects are needed
• context.read<Bloc>().add(Event()) for dispatching events
• context.watch<Bloc>().state for reactive rebuilds (inside build() only)

Workflow: Implementing State Management

Follow this sequential workflow when adding or updating a BLoC. Copy the checklist to track progress.

Task Progress

• Step 1: Define Events and States. Ensure they use Equatable with correct props or freezed.
• Step 2: Implement Async Operations. Verify that all async work follows the Loading → Success/Error pattern.
• Step 3: Refactor UI. Ensure there is no orchestration or business logic in UI widgets; they must only dispatch events.
• Step 4: Verify Data Sources. Ensure no SDK/API calls exist outside DataSources.
• Step 5: Review Design Tokens. Ensure zero hardcoded colors, spacing, or typography are used.
• Step 6: Format Code. Ensure the code is formatted with dart format.

Dependency Injection

• Use injectable for dependency injection and service location
• Standardized Injection:
  • Use @injectable for screen-specific BLoCs to ensure a fresh instance per screen access.
  • Use @lazySingleton for global or shared BLoCs (e.g., AuthBloc, ThemeBloc, SettingsBloc, PasswordBloc).
• Organize blocs logically by feature and ensure strict separation of concerns

Navigation & Routing

• Dynamic Routes: STRICTLY prohibit hardcoded route strings in GoRouter configuration. Use static constants in AppRoutes.
• Centralized BLoCs: BLoC providers MUST be injected via ShellRoute or BlocProvider in app_router.dart when shared across multiple screens or within a feature branch.
• No Local Providers: Avoid BlocProvider in individual screen build() methods if the BLoC is needed by a feature set.
• Primitive Route Arguments: STRICTLY prohibit passing complex objects (BLoCs, ChangeNotifiers, Entity instances) as route arguments. Pass only primitive IDs/Keys and fetch data in the destination screen using Repository or Bloc injection.

Source: dhruvanbhalara/skills — distributed by TomeVault.