Write, review, or improve SwiftUI code. Use for SwiftUI features/refactors, state management, view composition, performance, concurrency, modern Apple APIs, or native UI quality.
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Write, review, or improve SwiftUI code. Use for SwiftUI features/refactors, state management, view composition, performance, concurrency, modern Apple APIs, or native UI quality.
SwiftUI Expert
Overview
Use this skill to build, review, or improve SwiftUI features with correct state management, modern API usage, Swift concurrency best practices, optimal view composition, and iOS 26+ Liquid Glass styling. Prioritize native APIs, Apple design guidance, and performance-conscious patterns. This skill focuses on facts and best practices without enforcing specific architectural patterns.
Workflow Decision Tree
1) Review existing SwiftUI code
Check property wrapper usage against the selection guide (see references/state-management.md)
Verify modern API usage (see references/modern-apis.md)
Verify view composition follows extraction rules (see references/view-structure.md)
Check performance patterns are applied (see references/performance-patterns.md)
Verify list patterns use stable identity (see references/list-patterns.md)
Check animation patterns for correctness (see references/animation-basics.md, references/animation-transitions.md)
Inspect Liquid Glass usage for correctness and consistency (see references/liquid-glass.md)
Validate iOS 26+ availability handling with sensible fallbacks
2) Improve existing SwiftUI code
Audit state management for correct wrapper selection (prefer @Observable over ObservableObject)
Replace deprecated APIs with modern equivalents (see references/modern-apis.md)
Extract complex views into separate subviews (see )
references/view-structure.md
Refactor hot paths to minimize redundant state updates (see references/performance-patterns.md)
Ensure ForEach uses stable identity (see references/list-patterns.md)
Improve animation patterns (use value parameter, proper transitions, see references/animation-basics.md, references/animation-transitions.md)
Suggest image downsampling when UIImage(data:) is used (as optional optimization, see references/image-optimization.md)
Adopt Liquid Glass only when explicitly requested by the user
3) Implement new SwiftUI feature
Design data flow first: identify owned vs injected state (see references/state-management.md)
Use modern APIs (no deprecated modifiers or patterns, see references/modern-apis.md)
Use @Observable for shared state (with @MainActor if not using default actor isolation)
Structure views for optimal diffing (extract subviews early, keep views small, see references/view-structure.md)
Separate business logic into testable models (see references/layout-best-practices.md)
Use correct animation patterns (implicit vs explicit, transitions, see references/animation-basics.md, references/animation-transitions.md, references/animation-advanced.md)
Apply glass effects after layout/appearance modifiers (see references/liquid-glass.md)
Gate iOS 26+ features with #available and provide fallbacks
Core Guidelines
State Management
Always prefer @Observable over ObservableObject for new code
Mark @Observable classes with @MainActor unless using default actor isolation
Always mark @State and @StateObject as private (makes dependencies clear)
Never declare passed values as @State or @StateObject (they only accept initial values)
Use @State with @Observable classes (not @StateObject)
@Binding only when child needs to modify parent state
@Bindable for injected @Observable objects needing bindings
Use let for read-only values; var + .onChange() for reactive reads
Legacy: @StateObject for owned ObservableObject; @ObservedObject for injected
Nested ObservableObject doesn't work (pass nested objects directly); @Observable handles nesting fine
Modern APIs
Use foregroundStyle() instead of foregroundColor()
Use clipShape(.rect(cornerRadius:)) instead of cornerRadius()
Use Tab API instead of tabItem()
Use Button instead of onTapGesture() (unless need location/count)
Use NavigationStack instead of NavigationView
Use navigationDestination(for:) for type-safe navigation
Use two-parameter or no-parameter onChange() variant
Use ImageRenderer for rendering SwiftUI views
Use .sheet(item:) instead of .sheet(isPresented:) for model-based content
Sheets should own their actions and call dismiss() internally
Use ScrollViewReader for programmatic scrolling with stable IDs
Avoid UIScreen.main.bounds for sizing
Avoid GeometryReader when alternatives exist (e.g., containerRelativeFrame())
Swift Best Practices
Use modern Text formatting (.format parameters, not String(format:))
Use localizedStandardContains() for user-input filtering (not contains())
Prefer static member lookup (.blue vs Color.blue)
Use .task modifier for automatic cancellation of async work
Use .task(id:) for value-dependent tasks
View Composition
Prefer modifiers over conditional views for state changes (maintains view identity)
Extract complex views into separate subviews for better readability and performance
Keep views small for optimal performance
Keep view body simple and pure (no side effects or complex logic)
Use @ViewBuilder functions only for small, simple sections
Prefer @ViewBuilder let content: Content over closure-based content properties
Separate business logic into testable models (not about enforcing architectures)
Action handlers should reference methods, not contain inline logic
Use relative layout over hard-coded constants
Views should work in any context (don't assume screen size or presentation style)
Performance
Pass only needed values to views (avoid large "config" or "context" objects)
Eliminate unnecessary dependencies to reduce update fan-out
Check for value changes before assigning state in hot paths
Avoid redundant state updates in onReceive, onChange, scroll handlers
Minimize work in frequently executed code paths
Use LazyVStack/LazyHStack for large lists
Use stable identity for ForEach (never .indices for dynamic content)
Ensure constant number of views per ForEach element
Avoid inline filtering in ForEach (prefilter and cache)
Avoid AnyView in list rows
Consider POD views for fast diffing (or wrap expensive views in POD parents)
Suggest image downsampling when UIImage(data:) is encountered (as optional optimization)
Avoid layout thrash (deep hierarchies, excessive GeometryReader)
Gate frequent geometry updates by thresholds
Use Self._printChanges() to debug unexpected view updates
Animations
Use .animation(_:value:) with value parameter (deprecated version without value is too broad)
Use withAnimation for event-driven animations (button taps, gestures)
Prefer transforms (offset, scale, rotation) over layout changes (frame) for performance
Transitions require animations outside the conditional structure
Custom Animatable implementations must have explicit animatableData
Use .phaseAnimator for multi-step sequences (iOS 17+)
Use .keyframeAnimator for precise timing control (iOS 17+)
Animation completion handlers need .transaction(value:) for reexecution
Implicit animations override explicit animations (later in view tree wins)
Liquid Glass (iOS 26+)
Only adopt when explicitly requested by the user.
Use native glassEffect, GlassEffectContainer, and glass button styles
Wrap multiple glass elements in GlassEffectContainer
Apply .glassEffect() after layout and visual modifiers
Use .interactive() only for tappable/focusable elements
Use glassEffectID with @Namespace for morphing transitions
Quick Reference
Property Wrapper Selection (Modern)
Wrapper
Use When
@State
Internal view state (must be private), or owned @Observable class
@Binding
Child modifies parent's state
@Bindable
Injected @Observable needing bindings
let
Read-only value from parent
var
Read-only value watched via .onChange()
Legacy (Pre-iOS 17):
Wrapper
Use When
@StateObject
View owns an ObservableObject (use @State with @Observable instead)
@ObservedObject
View receives an ObservableObject
Modern API Replacements
Deprecated
Modern Alternative
foregroundColor()
foregroundStyle()
cornerRadius()
clipShape(.rect(cornerRadius:))
tabItem()
Tab API
onTapGesture()
Button (unless need location/count)
NavigationView
NavigationStack
onChange(of:) { value in }
onChange(of:) { old, new in } or onChange(of:) { }
