flutter-performance

Flutter Performance

Full reference: template.md

Key rules

Const everything possible

• Mark widgets, constructors, lists, and maps const wherever valid — eliminates rebuild.
• Use const in itemBuilder callbacks for static children.

Minimize rebuild scope

• Extract frequently-rebuilding children into separate StatelessWidgets.
• Use BlocSelector instead of BlocBuilder when only a subset of state is needed.
• RepaintBoundary around independently-animating subtrees (maps, charts, video).

List performance

• ListView.builder + ListView.separated for large lists — never ListView(children: []).
• Set itemExtent or prototypeItem on ListView.builder when all items have the same height (skips layout).
• CachedNetworkImage for all remote images — AppCachedImage wrapper.

Isolates

• Offload JSON decoding > 1 MB with compute(jsonDecode, rawString).
• Offload sorting/filtering large lists with compute().
• Never do heavy computation on the main isolate.

Image optimization

• Use width/height on AppCachedImage to constrain decode size.
• Use memCacheWidth/memCacheHeight for thumbnails.
• Prefer WebP over PNG for large assets.

Anti-patterns

• setState in build() — always causes infinite rebuild.
• MediaQuery.of(context) deep in the tree — cache at page level.
• Creating TextEditingController / AnimationController in build() — use State.
• Opacity(opacity: 0) to hide — use Visibility or Offstage.

Co-load with

• flutter-common-widgets — App widgets are already optimized
• flutter-animations — animations must not drop frames