Swiftui Expert Skill

SwiftUI Expert Skill

Overview

Use this skill to build, review, or improve SwiftUI features with correct state management, 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 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 (see references/state-management.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)
• Structure views for optimal diffing (extract subviews early, see references/view-structure.md)
• Keep business logic in services and models for testability (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

• @State must be private; use for internal view state
• @Binding only when a child needs to modify parent state
• @StateObject when view creates the object; @ObservedObject when injected
• iOS 17+: Use @State with @Observable classes; use @Bindable for injected observables needing bindings
• Use let for read-only values; var + .onChange() for reactive reads
• Never pass values into @State or @StateObject — they only accept initial values
• Nested ObservableObject doesn't propagate changes — pass nested objects directly; @Observable handles nesting fine

View Composition

• Extract complex views into separate subviews for better readability and performance
• Prefer modifiers over conditional views for state changes (maintains view identity)
• 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
• Keep business logic in services and models; views should orchestrate UI flow
• Action handlers should reference methods, not contain inline logic
• 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