---
name: flutter-widgets
description: "Principles for maintainable UI components. Use when building, refactoring, or reviewing Flutter widget implementations for maintainability. (triggers: **_page.dart, **_screen.dart, **/widgets/**, StatelessWidget, const, Theme, ListView)"
---

# UI & Widgets

## **Priority: P1 (OPERATIONAL)**

Standards for building reusable, performant Flutter widgets and UI components.

- **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 a 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

- ❌ `setState(() { _orders = await repo.fetch(); })` — server/shared state belongs in a BLoC, not widget state
- ❌ Widget file over 80 lines without extracting private sub-widget classes — helper methods returning `Widget` are not a substitute
- ❌ `Key('submit-button')` inline in widget code — all keys must be constants defined in `widget_keys.dart`
- ❌ `Widget _buildHeader() { … }` helper methods — extract to a `const` `StatelessWidget` private class for proper rebuilding control

## Related Topics

performance | testing




---
Source attribution: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2026 SkillsHub Contributors

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.



# Mega AI Hub resource metadata

Creator / publisher: HoangNguyen0403
Original project: https://github.com/HoangNguyen0403/agent-skills-standard
Attribution basis: Original repository namespace preserved by package mirror

Fields of work: Development & Engineering, Product Management
Roles: Frontend Developer, Mobile Developer, Product Manager
Specialties: Frontend, Mobile
Tools: Flutter
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: a16a0453cf07492fd7d6286db1e5477c4bf692927a76f606b527840b8dcba129
Metadata reviewed: 2026-10-27
This metadata supersedes earlier Mega AI Hub catalog attribution. Original instruction and supporting files are preserved.