performance-patternslisted

# Performance Patterns Skill Best practices for Flutter performance with Impeller rendering, Riverpod 3.x, and DevTools profiling. ## When to Use - User mentions "slow screen" / "jank" / "frame drops" / "optimize" - Large APK/IPA size or slow startup - Widget rebuild overhead or animation stuttering - Questions about profiling, DevTools, or performance budgets --- ## Quick Reference: Common Problems | Problem | Symptom | Solution | |---------|---------|----------| | Excessive rebuilds | Slow UI, high CPU in profile | `const`, `select()`, split widgets | | Jank during scroll | Dropped frames, stuttering | `ListView.builder`, `itemExtent`, `RepaintBoundary` | | Large images | Memory pressure, OOM crashes | `cached_network_image`, resize, `precacheImage` | | Large APK size | >30 MB download, slow install | `--split-per-abi`, deferred imports, tree shaking | | Slow startup | 3+ seconds cold start | Lazy init, deferred loading, reduce main() work | | Animation jank | <60 FPS during transitions | Impeller, `RepaintBoundary`, simplify painters | | Heavy computation | Frozen UI during processing | `Isolate.run()`, `compute()` | | Memory leaks | Growing memory, eventual crash | Dispose controllers, cancel subscriptions | --- ## Widget Rebuild Optimization ### Const Constructors ```dart // ❌ Rebuilds every frame — new instance each time @override Widget build(BuildContext context) { return Padding( padding: EdgeInsets.all(16), // new EdgeInsets each build child: Col