SwiftUI Expert

Build declarative iOS UIs with correct state flow and smooth animations.

State management

Pick the right property wrapper:

• @State — local, view-owned, value-type state.
• @Binding — a two-way reference to state owned elsewhere.
• @Observable (Observation framework) — model objects; views observe only the properties they read.
• @Environment — dependency injection down the tree.

@Observable final class CounterModel { var count = 0 }

struct CounterView: View {
  @State private var model = CounterModel()
  var body: some View {
    Button("Count: \(model.count)") { model.count += 1 }
  }
}

View composition

• Keep body small; extract subviews for reuse and to scope invalidation.
• Pass minimal data into subviews so only the affected views re-render.
• Use @ViewBuilder helpers instead of giant nested closures.

Animations

• Drive animation from state: withAnimation { model.expanded.toggle() }.
• Prefer .animation(_:value:) scoped to a specific value over implicit global animations.
• Use matchedGeometryEffect for shared-element transitions; transition for insert/remove.

Lists and performance

• Use LazyVStack/List for large collections so rows render on demand.
• Give items stable ids; unstable ids cause flicker and lost state.
• Avoid heavy work in body; compute in the model.

Accessibility

• Add accessibilityLabel/accessibilityValue; group related elements with accessibilityElement(children:).
• Respect Dynamic Type — use system fonts and avoid fixed frames that clip text.
• Support reduceMotion and sufficient contrast.

Rules

• Never mutate state during body evaluation — it loops or warns.
• Do async work in .task {}, which cancels on disappear, not onAppear + Task.
• Keep models testable and free of view types.

Edge cases

• Long-lived state: lift it above the view that can disappear, or it resets.
• Keyboard avoidance and safe areas: use safeAreaInset and scrollDismissesKeyboard.
• Previews: use sample data and multiple #Previews for states and Dynamic Type sizes.