ios-performance-profiler

Performance Profiler

View Identity & Diffing

• Stable, persistent identity (Identifiable with stable id, avoid random UUIDs in rows)
• Prefer value types + structural identity over class reference identity when possible
• Avoid .id() unless absolutely necessary (use stable keys instead)

Body Computation & Redraws

• No heavy work (network, decoding, sorting, filtering) inside body
• Expensive derived state computed once and stored (.onAppear, ViewModel, or memoized computed property)
• @State, @Bindable, @Observable properties are narrowly scoped
• Child views extracted when parent state changes frequently
• Prefer @Observable (Observation framework) over @ObservableObject / @Published for new code — finer-grained invalidation, less boilerplate

Lists & Large Collections

• Use List / LazyVStack / LazyHGrid instead of ScrollView + ForEach + VStack
• Rows are lightweight; avoid @StateObject / @ObservedObject inside row bodies
• Use stable Identifiable conformance or explicit id: key path

Concurrency & Main Actor (Swift 6 era)

• @MainActor used appropriately on view-bound types (avoid overuse → thread hops)
• Nonisolated properties / computed vars when safe
• Actors used for model / service layers; avoid @MainActor on pure data models
• No data races when using @Observable types across concurrency domains
• Prefer .task over .onAppear for async work (automatic cancellation on view disappear, structured concurrency)

Environment & State Propagation

• Avoid injecting large @Observable objects via @Environment when only a small slice of state is needed — extract a child view that reads only what it needs
• Minimize over-subscription from EnvironmentObject — split into focused, smaller observable types if necessary

Memory & Retain Cycles

• [weak self] in async / escaping closures that capture self
• @StateObject for view-owned view models (not in List rows)
• Remote images use proper caching (AsyncImage with cache, or Kingfisher / Nuke)
• Downscale images to display size before rendering (.resizable() + .frame() alone doesn't reduce memory)
• Use preparingThumbnail(of:) for large images
• Avoid long-lived strong references in @Observable / @ObservableObject