Flutter Clean Architecture Skill

Generate Flutter applications following Clean Architecture principles with feature-first organization, Riverpod for state management, and functional error handling using fpdart.

Includes Dio + Retrofit for type-safe REST API calls.

Core Principles

Architecture: Clean Architecture (Feature-First)

• Domain layer: Pure business logic, no dependencies
• Data layer: Data sources, repositories implementation, data models
• Presentation layer: UI, state management, view models

Dependency Rule: Presentation → Domain ← Data (Domain has no external dependencies)

State Management: Riverpod 3.0+ with code generation

Note: Riverpod 3.0+ & Freezed 3.0+ Required

Riverpod 3.0+: The XxxRef types (like DioRef, UserRepositoryRef, etc.) have been removed in favor of a unified Ref type.

Riverpod 2.x (Legacy):

@riverpod
SomeType someType(SomeTypeRef ref) { ... }

Riverpod 3.x+ (Current):

@riverpod
SomeType someType(Ref ref) { ... }

Freezed 3.0+: Two major breaking changes from v2:

1. Required sealed / abstract Keyword

All classes using factory constructors now require either sealed or abstract keyword.

Class Type	Freezed 2.x (Legacy)	Freezed 3.x+ (Current)
Single constructor	class Person	abstract class Person
Union type (multiple constructors)	class Result	sealed class Result

Freezed 2.x (Legacy) - Single Constructor:

@freezed
class Person with _$Person {
  const factory Person({
    required String firstName,
    required String lastName,
  }) = _Person;
}

Freezed 3.x+ (Current) - Single Constructor:

@freezed
abstract class Person with _$Person {
  const factory Person({
    required String firstName,
    required String lastName,
  }) = _Person;
}

Freezed 2.x (Legacy) - Union Type:

@freezed
class Result with _$Result {
  const factory Result.success(String data) = Success;
  const factory Result.error(String message) = Error;
}

Freezed 3.x+ (Current) - Union Type:

@freezed
sealed class Result with _$Result {
  const factory Result.success(String data) = Success;
  const factory Result.error(String message) = Error;
}

2. Pattern Matching (.map / .when Removed)

Freezed 3.x no longer generates .map/.when extensions. Use Dart 3's native pattern matching instead.

Freezed 2.x (Legacy) - Using .map:

final model = Model.first('42');
final res = model.map(
  first: (value) => 'first ${value.a}',
  second: (value) => 'second ${value.b} ${value.c}',
);

Freezed 3.x+ (Current) - Using switch expression:

final model = Model.first('42');
final res = switch (model) {
  First(:final a) => 'first $a',
  Second(:final b, :final c) => 'second $b $c',
};

Required versions: This skill requires Riverpod 3.0+ and Freezed 3.0+. Check your version with flutter pub deps | grep riverpod.

Error Handling: fpdart's Either<Failure, T> for functional error handling

Networking: Dio + Retrofit for type-safe REST API calls

Project Structure

lib/
├── core/
│   ├── constants/
│   │   ├── api_constants.dart
│   ├── errors/
│   │   ├── failures.dart
│   │   └── network_exceptions.dart
│   ├── network/
│   │   ├── dio_provider.dart
│   │   └── interceptors/
│   │       ├── auth_interceptor.dart
│   │       ├── logging_interceptor.dart
│   │       └── error_interceptor.dart
│   ├── storage/
│   ├── services/
│   ├── router/
│   │   └── app_router.dart
│   └── utils/
├── shared/ 
├── features/
│   └── [feature_name]/
│       ├── data/
│       │   ├── models/
│       │   │   └── [entity]_model.dart
│       │   ├── datasources/
│       │   │   └── [feature]_api_service.dart
│       │   └── repositories/
│       │       └── [feature]_repository_impl.dart
│       ├── domain/
│       │   ├── entities/
│       │   ├── repositories/
│       │   │   └── [feature]_repository.dart
│       │   └── usecases/
│       │       └── [action]_usecase.dart
│       └── presentation/
│           ├── providers/
│           │   └── [feature]_provider.dart
│           ├── screens/
│           │   └── [feature]_screen.dart
│           └── widgets/
│               └── [feature]_widget.dart
└── main.dart

Quick Start

1. Domain Layer (Entities, Repository Interfaces, UseCases)

// Entity
@freezed
sealed class User with _$User {
  const factory User({
    required String id,
    required String name,
    required String email,
  }) = _User;
}

// Repository Interface
abstract class UserRepository {
  Future<Either<Failure, User>> getUser(String id);
}

// UseCase
class GetUser {
  final UserRepository repository;
  GetUser(this.repository);
  Future<Either<Failure, User>> call(String id) => repository.getUser(id);
}

2. Data Layer (Models, API Service, Repository Implementation)

// Model with JSON serialization
@freezed
sealed class UserModel with _$UserModel {
  const UserModel._();
  const factory UserModel({
    required String id,
    required String name,
    required String email,
  }) = _UserModel;

  factory UserModel.fromJson(Map<String, dynamic> json) => _$UserModelFromJson(json);

  User toEntity() => User(id: id, name: name, email: email);
}

// Retrofit API Service
@RestApi()
abstract class UserApiService {
  factory UserApiService(Dio dio) = _UserApiService;

  @GET('/users/{id}')
  Future<UserModel> getUser(@Path('id') String id);
}

// Repository Implementation
class UserRepositoryImpl implements UserRepository {
  final UserApiService apiService;

  @override
  Future<Either<Failure, User>> getUser(String id) async {
    try {
      final userModel = await apiService.getUser(id);
      return Right(userModel.toEntity());
    } on DioException catch (e) {
      return Left(Failure.network(NetworkExceptions.fromDioError(e).message));
    }
  }
}

3. Presentation Layer (Providers, Screens)

// Provider
@riverpod
UserApiService userApiService(Ref ref) {
  return UserApiService(ref.watch(dioProvider));
}

@riverpod
UserRepositoryImpl userRepository(Ref ref) {
  return UserRepositoryImpl(ref.watch(userApiServiceProvider));
}

@riverpod
class UserNotifier extends _$UserNotifier {
  @override
  FutureOr<User?> build() => null;

  Future<void> fetchUser(String id) async {
    state = const AsyncLoading();
    final result = await ref.read(userRepositoryProvider).getUser(id);
    state = result.fold(
      (failure) => AsyncError(failure, StackTrace.current),
      (user) => AsyncData(user),
    );
  }
}

// Screen
class UserScreen extends ConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final userState = ref.watch(userNotifierProvider);

    return Scaffold(
      body: userState.when(
        data: (user) => Text('Hello ${user?.name}'),
        loading: () => const CircularProgressIndicator(),
        error: (e, _) => Text('Error: $e'),
      ),
    );
  }
}

Code Generation

# Generate all files
dart run build_runner build --delete-conflicting-outputs

# Watch mode
dart run build_runner watch --delete-conflicting-outputs

Best Practices

DO:

• Keep domain entities pure (no external dependencies)
• Use freezed with sealed keyword for immutable data classes
• Handle all error cases with Either<Failure, T>
• Use riverpod_generator with unified Ref type
• Separate models (data) from entities (domain)
• Place business logic in use cases, not in widgets
• Use Retrofit for type-safe API calls
• Handle DioException in repositories with NetworkExceptions
• Use interceptors for cross-cutting concerns (auth, logging)

DON'T:

• Import Flutter/HTTP libraries in domain layer
• Mix presentation logic with business logic
• Use try-catch directly in widgets when using Either
• Create god objects or god providers
• Skip the repository pattern
• Use legacy XxxRef types in new code

Common Issues

Issue	Solution
Build runner conflicts	dart run build_runner clean && dart run build_runner build --delete-conflicting-outputs
Provider not found	Ensure generated files are imported and run build_runner
Either not unwrapping	Use fold(), match(), or getOrElse() to extract values
XxxRef not found	Use unified Ref type instead (Riverpod 3.x+)
sealed keyword error	Upgrade to Dart 3.3+ and Freezed 3.0+
.map / .when not found	Freezed 3.0+ removed these methods. Use Dart 3 switch expression pattern matching instead

Knowledge References

Primary Libraries (used in this skill):

• Flutter 3.19+: Latest framework features
• Dart 3.3+: Language features (patterns, records, sealed modifier)
• Riverpod 3.0+: State management with unified Ref type
• Dio 5.9+: HTTP client with interceptors
• Retrofit 4.9+: Type-safe REST API code generation
• freezed 3.0+: Immutable data classes with code generation
• json_serializable 6.x: JSON serialization
• go_router 14.x+: Declarative routing
• fpdart: Functional error handling with Either type

References

• quick_start.md - Step-by-step feature creation workflow
• data_layer.md - Models, Retrofit API services, Repositories
• presentation_layer.md - Providers, Screens, Widgets patterns
• network_setup.md - Dio provider, Interceptors, Network exceptions
• error_handling.md - Either patterns, Failure types, Error strategies
• retrofit_patterns.md - Complete Retrofit API request patterns