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name: flutter-widgets description: Build maintainable Flutter UI components with composition and theming. Use when changing widget implementation; defer animation-only changes and widget-test authoring. metadata: triggers: files: - '_page.dart' - '_screen.dart' - '/widgets/' keywords: - StatelessWidget - const - Theme - ListView

UI & Widgets

Priority: P1 (HIGH)

• State: Use StatelessWidget by default. StatefulWidget only for local state/controllers.
• Composition: Extract UI into small, atomic const widgets.
• Theming: Use Theme.of(context). No hardcoded colors.
• Layout: Use Flex + Gap/SizedBox.
• Widget Keys: All interactive elements must use keys from widget_keys.dart.
• File Size: If UI file exceeds ~80 lines, extract sub-widgets into private classes.
• Specialized:
• SelectionArea: For multi-widget text selection.
• InteractiveViewer: For zoom/pan.
• ListWheelScrollView: For pickers.
• IntrinsicWidth/Height: Avoid unless strictly required.
• Large Lists: Always use ListView.builder.

class AppButton extends StatelessWidget {
  final String label;
  final VoidCallback onPressed;
  const AppButton({super.key, required this.label, required this.onPressed});

  @override
  Widget build(BuildContext context) => ElevatedButton(onPressed: onPressed, child: Text(label));
}

Anti-Patterns

• No setState for server state: Server or shared state belongs in BLoC, not widget state.
• No widget file over 80 lines without extraction: Extract sub-widgets into private classes.
• No inline Key strings: All keys must constants defined in widget_keys.dart.
• No _buildXxx() helper methods: Extract to const StatelessWidget private class.
• No manual widget repetition: When 3+ sibling widgets of the same type differ only in data (e.g., radio buttons, tabs), map over a list instead. Put display labels inside the value object or a companion map so adding an option requires no UI change.

References

• performance | testing

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• Extract
• interactive elements
• into private