# Flutter Widgets

> Build maintainable Flutter UI components with composition and theming. Use when changing widget implementation; defer animation-only changes and widget-test authoring.

- Skill: `hoangnguyen0403/flutter-widgets` (Agent Skill, multi-file: 2 files)
- Install (CLI): `npx skillmds@latest add hoangnguyen0403/flutter-widgets`
- Raw SKILL.md: https://api.skillmd.com/api/skills/hoangnguyen0403/flutter-widgets/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: HoangNguyen0403 (https://skillmd.com/u/hoangnguyen0403)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/hoangnguyen0403/flutter-widgets

---

# 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`.

```dart
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