flutter-performancelisted

# Flutter performance Verified 2026-09-25 against docs.flutter.dev/perf (Flutter 3.47: Impeller is the default renderer on iOS, Android API 29+, macOS, Windows and Linux; not web). A frame has **~16 ms at 60 Hz (~8 ms at 120 Hz)**. Almost every real Flutter performance problem is self-inflicted: too-wide rebuilds, work in `build()`, eager lists, full-resolution images, or CPU work on the UI isolate. The engine (Impeller) is rarely the bottleneck. ## Measure first - Profile in **profile mode on a real (ideally low-end) device**. Debug-mode numbers are meaningless. - Use DevTools Performance and the Timeline (frame times, jank), the Performance Overlay, and Memory (leaks, image cache). - Optimize when you see dropped frames, stuttering animations, or laggy scrolling. Otherwise write clear code first. No premature optimization. ## Rebuilds - Call `setState` as low in the tree as possible. State high up rebuilds everything below it. - Split big widgets into **small widget classes** (not helper methods, which rebuild with the parent). Use `const` constructors wherever possible; const widgets are skipped on rebuild. - Nothing expensive in `build()` (parsing, sorting, filtering, formatting big data). Do it in `initState`/`didUpdateWidget` (recompute only when input changed) or in the state layer. - In Riverpod/BLoC, watch only what the widget needs (`select`, `BlocSelector`, `context.select`) so unrelated state changes don't rebuild it. - Flutter Web is extra sensitive to deep