Flutter Architecture Patterns

class CounterController {
  int count = 0;
  
  // The Controller handles the logic
  void increment() {
    count++;
    // And manually tells the View to update
    update(); 
  }
}

lib/
├── main.dart            # Entry point
├── config/              # Routes, Themes
├── models/              # Data Models
│   └── user_model.dart
├── views/               # UI Screens & Widgets
│   ├── home_view.dart
│   └── widgets/
└── controllers/         # Business Logic
    └── home_controller.dart

class CounterViewModel {
  // Expose a stream of data (State)
  final _countController = StreamController<int>();
  Stream<int> get countStream => _countController.stream;
  
  int _count = 0;
  
  void increment() {
    _count++;
    // Add new value to the stream - View updates automatically
    _countController.add(_count);
  }
}

lib/
├── main.dart
├── core/                # Constants, Utils
├── models/              # Data Models
├── views/               # UI Layer
│   ├── login_view.dart
│   └── widgets/
├── viewmodels/          # State & Logic
│   └── login_vm.dart
└── services/            # API Calls, Local Storage

// Domain Layer: Pure Dart, no Flutter dependencies
class GetUserUseCase {
  final UserRepository repository;

  GetUserUseCase(this.repository);

  // Executes a specific business rule
  Future<User> execute(String userId) async {
    // Can add validation or other logic here
    if (userId.isEmpty) throw InvalidIdException();
    
    return await repository.getUser(userId);
  }
}

lib/
├── main.dart
├── core/                # Errors, Network, Utils
├── config/              # Routes, Theme
└── features/            # Feature-based
    └── auth/
        ├── data/        # Repo Impl, Data Sources, Models
        │   ├── datasources/
        │   ├── models/
        │   └── repositories/
        ├── domain/      # Entities, Repo Interfaces, UseCases
        │   ├── entities/
        │   ├── repositories/
        │   └── usecases/
        └── presentation/# BLoC/Cubit, Pages, Widgets
            ├── bloc/
            ├── pages/
            └── widgets/

// Domain Entity with self-contained validation logic
class EmailAddress extends ValueObject<String> {
  @override
  final Either<ValueFailure<String>, String> value;

  // Private constructor
  const EmailAddress._(this.value);

  // Factory constructor that validates on creation
  factory EmailAddress(String input) {
    return EmailAddress._(
      validateEmailAddress(input),
    );
  }
}

lib/
├── main.dart
├── domain/              # Enterprise Business Rules
│   ├── auth/
│   │   ├── value_objects.dart
│   │   └── i_auth_facade.dart
│   └── core/
├── infrastructure/      # Interface Adapters
│   ├── auth/
│   │   ├── auth_facade_impl.dart
│   │   └── user_dtos.dart
│   └── core/
├── application/         # Application Business Rules
│   └── auth/
│       ├── sign_in_form_bloc.dart
│       └── auth_bloc.dart
└── presentation/        # Frameworks & Drivers
    ├── sign_in/
    └── app_widget.dart