flutter-coding

Flutter Coding

Match the project's existing conventions. When uncertain, read 2-3 existing widgets to infer the local style. Check pubspec.yaml for Flutter/Dart version and dependencies, and the project's state-management package (Provider, Riverpod, Bloc) or service locator (GetIt) before introducing a new pattern. These defaults apply only when the project has no established convention. For Dart language rules (null safety, async, records, patterns), see the dart-coding skill.

Never rules

These are unconditional. They prevent rebuild storms, corrupted state, and lifecycle bugs regardless of project style.

• Never use a helper function that returns Widget -- helper functions skip the const constructor cache and rebuild on every parent build. Promote to a StatelessWidget so Flutter can short-circuit identical instances via ==.

// Wrong: rebuilds every time the enclosing build runs
Widget _buildHeader(String title) {
  return Padding(
    padding: const EdgeInsets.all(16),
    child: Text(title, style: const TextStyle(fontSize: 24)),
  );
}

// Correct: a const StatelessWidget caches via instance equality
class _Header extends StatelessWidget {
  const _Header({required this.title});
  final String title;

  @override
  Widget build(BuildContext context) {
    return Padding(
      padding: const EdgeInsets.all(16),
      child: Text(title, style: const TextStyle(fontSize: 24)),
    );
  }
}

• Never pass mutable arguments where const constructors would work -- const Text('hi') short-circuits rebuilds via instance equality. Prefer const literals everywhere they apply.

// Wrong: a fresh Text every rebuild, even though args never change
Text('Save', style: TextStyle(fontWeight: FontWeight.bold))

// Correct: const literal is cached
const Text('Save', style: TextStyle(fontWeight: FontWeight.bold))

• Never extend Scaffold, Container, or other concrete widgets -- compose. Pass child widgets in via constructor, route events up via callbacks, and pass state down through fields. Inheritance from concrete widgets fights the framework.