flutter-performance

name	flutter-performance
description	Performance optimization for Flutter apps. Use when optimizing lists, build methods, const/keys, images, RepaintBoundary, isolates, or profiling with DevTools.

Flutter Performance

Lists

• ListView.builder / GridView.builder / SliverList for large lists — never Column/Row with many children
• const constructors for list item widgets
• Pagination: load in chunks, combine with builder
• Lazy loading: load on demand (scroll/visibility)

Build Methods

• No expensive work in build() — move to initState, didChangeDependencies, or cached values
• Scope rebuilds: Builder, ValueListenableBuilder, StreamBuilder, BlocBuilder
• Extract frequently rebuilt subtrees into separate widget classes

Const & Keys

• const constructors for static widgets — reused across rebuilds
• Keys for widgets that maintain identity across reorders: ValueKey, ObjectKey, UniqueKey

Images

• Image.asset — cached automatically
• Network images: cached_network_image package
• Don't reload same image on every rebuild

RepaintBoundary

• Wrap complex custom painters — isolates repaint region from siblings/parent
• Adds a compositing layer; profile before/after to validate benefit

Isolates

• compute() for CPU-intensive work: JSON parsing, image processing, batch transforms
• Function and argument must be top-level or static (isolate can't share references)

Data Structures

• Right structure for the job: List vs Set vs Map, growable vs fixed
• Prefer O(1)/O(log n) over O(n) at scale
• Cache expensive computations when inputs don't change

Profiling

• Flutter DevTools: Timeline, CPU profiler, memory view
• Identify: build time, layout, paint, rasterize bottlenecks
• Profile before/after optimizations and periodically during development