/flutter-expert

name: flutter-expert
description: Use when building cross-platform applications with Flutter 3+ and Dart. Invoke for widget development, Riverpod/Bloc state management, GoRouter navigation, platform-specific implementations, performance optimization.
license: MIT
metadata:
  author: https://github.com/Jeffallan
  version: "1.1.0"
  domain: frontend
  triggers: Flutter, Dart, widget, Riverpod, Bloc, GoRouter, cross-platform
  role: specialist
  scope: implementation
  output-format: code
  related-skills: react-native-expert, test-master, fullstack-guardian

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)

// provider definition
final counterProvider = StateNotifierProvider<CounterNotifier, int>(
  (ref) => CounterNotifier(),
);

class CounterNotifier extends StateNotifier<int> {
  CounterNotifier() : super(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

// ❌ 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 `StateNotifier` 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

[Documentation](https://jeffallan.github.io/claude-skills/skills/frontend/flutter-expert/)