flutter

What this skill does

# Flutter Skill


---

## Project Structure

```
project/
├── lib/
│   ├── core/                           # Core utilities
│   │   ├── constants/                  # App constants
│   │   ├── extensions/                 # Dart extensions
│   │   ├── router/                     # go_router configuration
│   │   │   └── app_router.dart
│   │   └── theme/                      # App theme
│   │       └── app_theme.dart
│   ├── data/                           # Data layer
│   │   ├── models/                     # Freezed data models
│   │   ├── repositories/               # Repository implementations
│   │   └── services/                   # API services
│   ├── domain/                         # Domain layer
│   │   ├── entities/                   # Business entities
│   │   └── repositories/               # Repository interfaces
│   ├── presentation/                   # UI layer
│   │   ├── common/                     # Shared widgets
│   │   ├── features/                   # Feature modules
│   │   │   └── feature_name/
│   │   │       ├── providers/          # Riverpod providers
│   │   │       ├── widgets/            # Feature-specific widgets
│   │   │       └── feature_screen.dart
│   │   └── providers/                  # Global providers
│   ├── main.dart
│   └── app.dart
├── test/
│   ├── unit/                           # Unit tests
│   ├── widget/                         # Widget tests
│   └── integration/                    # Integration tests
├── pubspec.yaml
├── analysis_options.yaml
└── CLAUDE.md
```

---

## Riverpod State Management

### Provider Types
```dart
// Simple value provider
final appNameProvider = Provider<String>((ref) => 'My App');

// StateProvider for simple mutable state
final counterProvider = StateProvider<int>((ref) => 0);

// NotifierProvider for complex state logic
final userProvider = NotifierProvider<UserNotifier, User?>(() => UserNotifier());

// AsyncNotifierProvider for async operations
final usersProvider = AsyncNotifierProvider<UsersNotifier, List<User>>(
  () => UsersNotifier(),
);

// FutureProvider for simple async data
final configProvider = FutureProvider<Config>((ref) async {
  return await ref.watch(configServiceProvider).loadConfig();
});

// StreamProvider for real-time data
final messagesProvider = StreamProvider<List<Message>>((ref) {
  return ref.watch(messageServiceProvider).watchMessages();
});

// Family providers for parameterized data
final userByIdProvider = FutureProvider.family<User, String>((ref, userId) async {
  return await ref.watch(userRepositoryProvider).getUser(userId);
});
```

### Notifier Pattern
```dart
@riverpod
class Users extends _$Users {
  @override
  Future<List<User>> build() async {
    return await _fetchUsers();
  }

  Future<List<User>> _fetchUsers() async {
    final repository = ref.read(userRepositoryProvider);
    return await repository.getUsers();
  }

  Future<void> refresh() async {
    state = const AsyncLoading();
    state = await AsyncValue.guard(() => _fetchUsers());
  }

  Future<void> addUser(User user) async {
    final repository = ref.read(userRepositoryProvider);
    await repository.addUser(user);
    ref.invalidateSelf();
  }
}
```

### AsyncValue Handling
```dart
class UsersScreen extends ConsumerWidget {
  const UsersScreen({super.key});

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final usersAsync = ref.watch(usersProvider);

    return usersAsync.when(
      data: (users) => UsersList(users: users),
      loading: () => const Center(child: CircularProgressIndicator()),
      error: (error, stack) => ErrorDisplay(
        error: error,
        onRetry: () => ref.invalidate(usersProvider),
      ),
    );
  }
}

// Pattern matching alternative
Widget build(BuildContext context, WidgetRef ref) {
  final usersAsync = ref.watch(usersProvider);

  return switch (usersAsync) {
    AsyncData(:final value) => UsersList(users: value),
    AsyncLoading() => const LoadingIndicator(),
    AsyncError(:final error) => ErrorDisplay(error: error),
  };
}
```

### ref Methods
```dart
// watch - rebuilds when provider changes
final users = ref.watch(usersProvider);

// read - one-time read, no rebuild
void onButtonPressed() {
  ref.read(counterProvider.notifier).state++;
}

// listen - react to changes without rebuild
ref.listen(authProvider, (previous, next) {
  if (next == null) {
    context.go('/login');
  }
});

// invalidate - force refresh
ref.invalidate(usersProvider);

// keepAlive - prevent auto-dispose
final link = ref.keepAlive();
// Later: link.close() to allow disposal
```

---

## Freezed Data Models

### Model Definition
```dart
import 'package:freezed_annotation/freezed_annotation.dart';

part 'user.freezed.dart';
part 'user.g.dart';

@freezed
class User with _$User {
  const factory User({
    required String id,
    required String name,
    required String email,
    @Default(false) bool isActive,
    DateTime? createdAt,
  }) = _User;

  factory User.fromJson(Map<String, dynamic> json) => _$UserFromJson(json);
}

// Union types for states
@freezed
sealed class AuthState with _$AuthState {
  const factory AuthState.initial() = _Initial;
  const factory AuthState.loading() = _Loading;
  const factory AuthState.authenticated(User user) = _Authenticated;
  const factory AuthState.unauthenticated() = _Unauthenticated;
  const factory AuthState.error(String message) = _Error;
}
```

### Using Freezed Unions
```dart
Widget build(BuildContext context, WidgetRef ref) {
  final authState = ref.watch(authProvider);

  return authState.when(
    initial: () => const SplashScreen(),
    loading: () => const LoadingScreen(),
    authenticated: (user) => HomeScreen(user: user),
    unauthenticated: () => const LoginScreen(),
    error: (message) => ErrorScreen(message: message),
  );
}
```

---

## go_router Navigation

### Router Configuration
```dart
final routerProvider = Provider<GoRouter>((ref) {
  final authState = ref.watch(authProvider);

  return GoRouter(
    initialLocation: '/',
    refreshListenable: authState,
    redirect: (context, state) {
      final isLoggedIn = authState.valueOrNull != null;
      final isLoggingIn = state.matchedLocation == '/login';

      if (!isLoggedIn && !isLoggingIn) return '/login';
      if (isLoggedIn && isLoggingIn) return '/';
      return null;
    },
    routes: [
      GoRoute(
        path: '/',
        builder: (context, state) => const HomeScreen(),
        routes: [
          GoRoute(
            path: 'user/:id',
            builder: (context, state) => UserScreen(
              userId: state.pathParameters['id']!,
            ),
          ),
        ],
      ),
      GoRoute(
        path: '/login',
        builder: (context, state) => const LoginScreen(),
      ),
    ],
    errorBuilder: (context, state) => ErrorScreen(error: state.error),
  );
});
```

### Navigation
```dart
// Navigate to route
context.go('/user/123');

// Push onto stack
context.push('/user/123');

// Pop current route
context.pop();

// Replace current route
context.pushReplacement('/home');

// Named routes
context.goNamed('user', pathParameters: {'id': '123'});
```

---

## Widget Patterns

### ConsumerWidget vs ConsumerStatefulWidget
```dart
// Stateless with Riverpod
class UserCard extends ConsumerWidget {
  const UserCard({super.key, required this.userId});

  final String userId;

  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final user = ref.watch(userByIdProvider(userId));
    return user.when(
      data: (user) => Card(child: Text(user.name)),
      loading: () => const CardSkeleton(),
      error: (e, _) => ErrorCard(error: e),
    );
  }
}

// Stateful with Riverpod
class SearchScreen extends ConsumerStatefulWidget {
  const SearchScreen({super.key});

  @override
  ConsumerState<SearchScreen> createState() => _SearchScreenState();
}

class _SearchScreenState extends ConsumerState<SearchScreen> {
  final _controller = TextEditingController();

  @override
  void dis