dart-flutter-patterns

# Dart/Flutter Patterns ## When to Use Use this skill when: - Starting a new Flutter feature and need idiomatic patterns for state management, navigation, or data access - Reviewing or writing Dart code and need guidance on null safety, sealed types, or async composition - Setting up a new Flutter project and choosing between BLoC, Riverpod, or Provider - Implementing secure HTTP clients, WebView integration, or local storage - Writing tests for Flutter widgets, Cubits, or Riverpod providers - Wiring up GoRouter with authentication guards ## How It Works This skill provides copy-paste-ready Dart/Flutter code patterns organized by concern: 1. **Null safety** — avoid `!`, prefer `?.`/`??`/pattern matching 2. **Immutable state** — sealed classes, `freezed`, `copyWith` 3. **Async composition** — concurrent `Future.wait`, safe `BuildContext` after `await` 4. **Widget architecture** — extract to classes (not methods), `const` propagation, scoped rebuilds 5. **State management** — BLoC/Cubit events, Riverpod notifiers and derived providers 6. **Navigation** — GoRouter with reactive auth guards via `refreshListenable` 7. **Networking** — Dio with interceptors, token refresh with one-time retry guard 8. **Error handling** — global capture, `ErrorWidget.builder`, crashlytics wiring 9. **Testing** — unit (BLoC test), widget (ProviderScope overrides), fakes over mocks ## Examples ```dart // Sealed state — prevents impossible states sealed class AsyncState<T> {} final class Loading<...