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

Required: Riverpod 3.0+ & Freezed 3.0+ — outdated patterns cause compile errors and hallucination loops.

Riverpod: use Ref ref (unified), NOT XxxRef ref

Freezed: use sealed class for union types, abstract class for single constructors

Pattern matching: use Dart 3 switch, NOT .map()/.when()
// Riverpod 3.x+
@riverpod
SomeType someType(Ref ref) { ... }

// Freezed 3.x+ — union type
@freezed
sealed class Result with _$Result { ... }

// Freezed 3.x+ — pattern matching
final res = switch (model) {
  First(:final a) => 'first $a',
  Second(:final b) => 'second $b',
};
Requires Dart 3.3+, Riverpod 3.0+, Freezed 3.0+. See migration_guide.md for full before/after examples.

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

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

Always use the latest stable versions of all libraries. Before adding dependencies, check pub.dev for the current versions of Riverpod, Freezed, Dio, Retrofit, fpdart, and go_router. Never default to outdated major versions (e.g. Riverpod 2.x, Freezed 2.x).

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

Build features in this order: Domain → Data → Presentation.

1. Domain Layer

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

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

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

2. Data Layer

@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);
}

@RestApi()
abstract class UserApiService {
  factory UserApiService(Dio dio) = _UserApiService;
  @GET('/users/{id}')
  Future<UserModel> getUser(@Path('id') String id);
}

3. Presentation Layer

@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),
    );
  }
}

See quick_start.md for the complete step-by-step workflow with all files.

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)
Validate API response data at the repository boundary
Use CachedNetworkImage instead of Image.network for external images
Pin API base URLs in config, enforce HTTPS

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
Pass raw external URLs to widgets without validation
Allow runtime-configuration of API base URLs from user input

Security

API responses and external content are untrusted input. Validate and sanitize at the data layer boundary to prevent injection and data corruption.

Response validation — Always validate API response structure before mapping to models. Retrofit + freezed handle typed deserialization, but wrap calls in try-catch and verify critical fields (IDs, URLs, numeric ranges) in the repository:

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

External URLs — Never pass raw API URLs directly to Image.network or WebView. Use CachedNetworkImage with error handling, and validate URL schemes:

CachedNetworkImage(
  imageUrl: user.avatarUrl ?? '',
  errorWidget: (_, __, ___) => const Icon(Icons.person),
  httpHeaders: {'Authorization': 'Bearer $token'},
)

Input sanitization — Sanitize user inputs before sending to API. Validate email format, trim strings, reject empty IDs, and encode query parameters properly.

Network hardening — Pin base URLs in AppConfig (not user-configurable at runtime), enforce HTTPS, use certificate pinning for production, and set conservative timeouts.

Read network_setup.md for the full interceptor setup and data_layer.md for validation patterns at the repository boundary.

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, Response validation
presentation_layer.md - Providers, Screens, Widgets, Secure image loading
network_setup.md - Dio provider, Interceptors, Network exceptions, Response validation
error_handling.md - Either patterns, Failure types, Error strategies
retrofit_patterns.md - Complete Retrofit API request patterns
provider_patterns.md - Advanced Riverpod patterns (pagination, caching, optimistic updates)
testing_guide.md - Unit, widget, and integration testing strategies
feature_examples.md - Complete Auth feature implementation
migration_guide.md - Riverpod 2→3 & Freezed 2→3 full before/after examples