| name | flutter-performance |
| description | Optimization standards for rebuilds and memory. Use when optimizing Flutter widget rebuilds, reducing memory usage, or improving rendering performance. (triggers: lib/presentation/**, pubspec.yaml, const, buildWhen, ListView.builder, Isolate, RepaintBoundary) |
Performance
Priority: P1 (OPERATIONAL)
Performance optimization techniques for smooth 60fps Flutter applications.
- Rebuilds: Use
const widgets and buildWhen / select for granular updates.
- Lists: Always use
ListView.builder for item recycling.
- Heavy Tasks: Use
compute() or Isolates for parsing/logic.
- Repaints: Use
RepaintBoundary for complex animations. Use debugRepaintRainbowEnabled to debug.
- Images: Use
CachedNetworkImage + memCacheWidth. precachePicture for SVGs.
- Keys: Provide
ValueKey for list items and stable IDs for reconciliation.
- Resource Cleanup: Dispose controllers/streams in
dispose().
- Pagination: Default to 20 items per page for network lists.
- Build Purity: Keep
build methods free of heavy work; move logic to BLoC/Application.
- Image Resizing: Always set
maxWidth/maxHeight when loading images.
Anti-Patterns
- ❌
setState() at the root/page level to update a single counter — use BlocBuilder with buildWhen or context.select() for granular rebuilds
- ❌ Sorting/filtering a list inside
build() — move heavy computation to BLoC or use compute()
- ❌ Non-
const leaf widgets that never change — always apply const to static widgets to skip reconciliation
- ❌
Column(children: items.map((e) => ItemWidget(e)).toList()) for large lists — use ListView.builder for item recycling
BlocBuilder<UserBloc, UserState>(
buildWhen: (p, c) => p.id != c.id,
builder: (context, state) => Text(state.name),
)
