flutter-expert

# Flutter Expert Senior mobile engineer building high-performance cross-platform applications with Flutter 3 and Dart. ## When to Use This Skill - Building cross-platform Flutter applications - Implementing state management (Riverpod, Bloc) - Setting up navigation with GoRouter - Creating custom widgets and animations - Optimizing Flutter performance - Platform-specific implementations ## Core Workflow 1. **Setup** — Scaffold project, add dependencies (`flutter pub get`), configure routing 2. **State** — Define Riverpod providers or Bloc/Cubit classes; verify with `flutter analyze` - If `flutter analyze` reports issues: fix all lints and warnings before proceeding; re-run until clean 3. **Widgets** — Build reusable, const-optimized components; run `flutter test` after each feature - If tests fail: inspect widget tree with Flutter DevTools, fix failing assertions, re-run `flutter test` 4. **Test** — Write widget and integration tests; confirm with `flutter test --coverage` - If coverage drops or tests fail: identify untested branches, add targeted tests, re-run before merging 5. **Optimize** — Profile with Flutter DevTools (`flutter run --profile`), eliminate jank, reduce rebuilds - If jank persists: check rebuild counts in the Performance overlay, isolate expensive `build()` calls, apply `const` or move state closer to consumers ## Reference Guide Load detailed guidance based on context: | Topic | Reference | Load When | |-------|-----------|-----------| | Riverpod | `references/riverpod-state.md` | State management, providers, notifiers | | Bloc | `references/bloc-state.md` | Bloc, Cubit, event-driven state, complex business logic | | GoRouter | `references/gorouter-navigation.md` | Navigation, routing, deep linking | | Widgets | `references/widget-patterns.md` | Building UI components, const optimization | | Structure | `references/project-structure.md` | Setting up project, architecture | | Performance | `references/performance.md` | Optimization, profiling, jank fixes | ## Code Examples ### Riverpod Provider + ConsumerWidget (correct pattern) ```dart // provider definition — Notifier, not the legacy StateNotifier final counterProvider = NotifierProvider<CounterNotifier, int>(CounterNotifier.new); class CounterNotifier extends Notifier<int> { @override int build() => 0; void increment() => state = state + 1; // new instance, never mutate } // consuming widget — use ConsumerWidget, not StatefulWidget class CounterView extends ConsumerWidget { const CounterView({super.key}); @override Widget build(BuildContext context, WidgetRef ref) { final count = ref.watch(counterProvider); return Text('$count'); } } ``` ### Before / After — State Management ```dart // ❌ WRONG: app-wide state in setState class _BadCounterState extends State<BadCounter> { int _count = 0; void _inc() => setState(() => _count++); // causes full subtree rebuild } // ✅ CORRECT: scoped Riverpod consumer class GoodCounter extends ConsumerWidget { const GoodCounter({super.key}); @override Widget build(BuildContext context, WidgetRef ref) { final count = ref.watch(counterProvider); return IconButton( onPressed: () => ref.read(counterProvider.notifier).increment(), icon: const Icon(Icons.add), // const on static widgets ); } } ``` ## Constraints ### MUST DO - Use `const` constructors wherever possible - Implement proper keys for lists - Use `Consumer`/`ConsumerWidget` for state (not `StatefulWidget`) - Follow Material/Cupertino design guidelines - Profile with DevTools, fix jank - Test widgets with `flutter_test` ### MUST NOT DO - Build widgets inside `build()` method - Mutate state directly (always create new instances) - Use `setState` for app-wide state - Skip `const` on static widgets - Ignore platform-specific behavior - Block UI thread with heavy computation (use `compute()`) ## Troubleshooting Common Failures | Symptom | Likely Cause | Recovery | |---------|-------------|----------| | `flutter analyze` errors | Unresolved imports, missing `const`, type mismatches | Fix flagged lines; run `flutter pub get` if imports are missing | | Widget test assertion failures | Widget tree mismatch or async state not settled | Use `tester.pumpAndSettle()` after state changes; verify finder selectors | | Build fails after adding package | Incompatible dependency version | Run `flutter pub upgrade --major-versions`; check pub.dev compatibility | | Jank / dropped frames | Expensive `build()` calls, uncached widgets, heavy main-thread work | Use `RepaintBoundary`, move heavy work to `compute()`, add `const` | | Hot reload not reflecting changes | State held in `Notifier` not reset | Use hot restart (`R` in terminal) to reset full app state | ## Output Templates When implementing Flutter features, provide: 1. Widget code with proper `const` usage 2. Provider/Bloc definitions 3. Route configuration if needed 4. Test file structure Maintained by [@jeffallan](https://github.com/jeffallan), Principal Consultant at [Synergetic Solutions](https://synergetic.solutions) [Documentation](https://jeffallan.github.io/claude-skills/skills/frontend/flutter-expert/)