flutter-performance

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),
)