Compose modern Flutter layouts and widgets idiomatically. Use when composing widget trees, managing layout constraints, or following idiomatic Flutter patterns.
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---
name: flutter-idiomatic-flutter
description: Compose modern Flutter layouts and widgets idiomatically. Use when composing widget trees, managing layout constraints, or following idiomatic Flutter patterns.
metadata:
triggers:
files:
- 'lib/presentation/**/*.dart'
- 'context.mounted'
keywords:
- SizedBox
- Gap
- composition
- shrink
---
# Idiomatic Flutter
## **Priority: P1 (OPERATIONAL)**
- **Async Gaps**: Check `if (context.mounted)` before using `BuildContext` after `await`.
- **Composition**: Extract complex UI into small widgets. Avoid deep nesting or large helper methods.
- **Layout**:
- Spacing: Prefer `spacing` parameter on `Row`/`Column` (Flutter 3.10+) over inserting `SizedBox`/`Gap` between children.
- Fallback: Use `Gap(n)` or `SizedBox` only when `spacing` cannot express the layout (e.g., conditional gaps).
- Empty UI: Use `const SizedBox.shrink()`.
- Intrinsic: Avoid `IntrinsicWidth/Height`; use `Stack` + `FractionallySizedBox` for overlays.
- Spacing: Use `Gap(n)` or `SizedBox` over `Padding` for simple gaps.
- Optimization: Use `ColoredBox`/`Padding`/`DecoratedBox` instead of `Container` when possible.
- Themes: Use extensions for `Theme.of(context)` access.
## Anti-Patterns
- **No BuildContext after await without mounted check**: Check `context.mounted` to prevent crashes across async gaps.
- **No _buildXxx() helper methods**: Extract to `const StatelessWidget` for proper rebuild control.
- **No direct controller access in widget**: Use BLoC or Signals to decouple UI from state.
- **No Container for empty space**: Use `const SizedBox.shrink()`.
