Swift Swiftui

SwiftUI Standards

Priority: P0 (CRITICAL)

Implementation Guidelines

State Management

• @State: @State for data owned by view (e.g., toggle, text input). Private.
• @Binding: @Binding for data passed down from parent to child. Two-way.
• @ObservedObject: @ObservedObject when receiving instance from external source.
• @StateObject: @StateObject when the view is creating the object instance — view owns lifecycle.
• @EnvironmentObject: @EnvironmentObject to inject data into the view's hierarchy via .environmentObject(). Shared across view hierarchy.

View Composition

• Extract Subviews: Views < 200 lines. Extract reusable components.
• View Modifiers: Chain modifiers for styling (.font(), .padding()).
• Custom Modifiers: Create ViewModifier for reusable styles.

Performance

• Avoid Heavy Computation: Use @State + .task() for async work.
• Equatable: Conform views to Equatable to prevent unnecessary re-renders.
• LazyStacks: LazyVStack/LazyHStack when displaying large number of views in scrolling container to load them only as they appear.

Anti-Patterns

• No @ObservedObject for owned objects: Use @StateObject.
• No logic in body: Move to computed properties or methods.
• No ! in View: Use if-let or nil coalescing.

References

• State & Binding

Canonical response anchors

When this skill applies, preserve the following domain terminology or equivalent concrete examples in the answer when relevant:

• @Binding for data passed down
• @ObservedObject when receiving
• @State for data owned
• inject data into the view's hierarchy
• large number of views
• load them only as they appear