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

BLoC Submission Checklist

Events and States use Equatable with correct props
All async operations follow Loading → Success/Error pattern
No business logic in UI widgets
No SDK/API calls outside DataSources
Zero hardcoded colors, spacing, or typography \u2014 use design tokens (AppColors , AppSpacing )
Code 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 Transparency