SwiftUI Expert Skill

Overview

Use this skill to build, review, or improve SwiftUI features with correct state management, native semantic UI structure, optimal view composition, and iOS 26+ Liquid Glass styling. Prioritize system containers and controls first, then layer visual polish and Liquid Glass on top of a correct hierarchy. 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)
• Inspect semantic container choice and native control usage (see references/native-semantic-ui.md)
• Verify modern API usage and deprecation replacements (see references/modern-apis.md)
• Verify text formatting and search patterns (see references/text-formatting.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
• For UI-focused changes, verify the result in simulator or previews against real app states before calling the screen complete

2) Improve existing SwiftUI code

• Audit state management for correct wrapper selection (see references/state-management.md)
• Replace stack-heavy custom screen structure with semantic containers where appropriate (see references/native-semantic-ui.md)
• Replace deprecated APIs with modern equivalents (see references/modern-apis.md)
• Replace legacy string/text formatting patterns (see references/text-formatting.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)
• Preserve existing user-facing actions, accessibility IDs, and test hooks during visual refactors
• Do not invent product behavior or ship placeholder/debug copy while redesigning UI
• Validate UI-focused changes one screen at a time in simulator before broad rollout
• Adopt Liquid Glass when requested by the user or when the product's design direction clearly calls for it, after hierarchy and semantics are correct

3) Implement new SwiftUI feature

• Design data flow first: identify owned vs injected state (see references/state-management.md)
• Select semantic containers and system controls before custom layout (see references/native-semantic-ui.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)
• Use supported app actions and real product states; don't invent buttons, copy, or flows that do not exist
• Apply Liquid Glass after hierarchy, accessibility, and interaction states are correct (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)

Native Semantics First

• Start with Form, Section, List, LabeledContent, NavigationStack, TextField, TextEditor, PasteButton, PhotosPicker, ShareLink, ToolbarItem, and ContentUnavailableView when they fit the interaction (see references/native-semantic-ui.md)
• Use Form and Section for settings, profile editing, and structured data-entry flows before building custom card stacks
• Use LabeledContent, plain text sections, or list rows for read-only content; do not mimic editable form fields for display-only data
• Prefer system row, disclosure, and destructive-action patterns over custom button bars when the semantics match
• Use raw VStack and HStack for screen-level structure only when semantic containers cannot express the UI cleanly
• Treat safeAreaInset as layout ownership, not just presentation. A custom bottom safeAreaInset is not equivalent to nav bars, toolbars, or an inputAccessoryView, especially when UIKit scroll views are involved.
• Be cautious using safeAreaInset for chat composers or other keyboard-attached bottom chrome over UIScrollView / UITableView / UICollectionView. It often breaks the illusion of full-bleed underlap while still failing to make the scroll viewport truly "attached" to the custom chrome.
• Do not feed measured safeAreaInset heights back into a UIKit scroll view unless there is no cleaner ownership boundary. That creates fragile bidirectional layout coupling and often diverges from keyboard/safe-area behavior.
• For transcript-style UIs that need Instagram/iMessage behavior, prefer UIKit-owned bottom chrome (inputAccessoryView, or a child view controller that owns both transcript and composer) over SwiftUI safeAreaInset.
• If a control must stay pinned above a chat composer, put that control in the same UIKit host/accessory coordinate system as the composer. Do not mirror the composer position back into SwiftUI with guessed bottom offsets when the transcript itself is UIKit-owned.
• If both the transcript and a pinned control depend on bottom chrome, derive both from the same native guide (keyboardLayoutGuide, accessory host constraints, or equivalent). Do not keep separate overlap formulas for the list and the control.
• Keep accessibility identifiers unique and preserve existing IDs during refactors unless tests and callers are updated together
• Do not remove working actions or ship placeholder/debug copy during visual changes
• Validate visual refactors in the simulator one screen at a time; treat simulator review as required, not optional
• Apply Liquid Glass after semantics and information hierarchy are correct

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+)

Treat Liquid Glass as a first-class iOS 26+ option when the user's request or the app's design direction calls for it.

• Use native glassEffect, GlassEffectContainer, and glass button styles
• Wrap multiple glass elements in GlassEffectContainer
• Apply glass only after hierarchy, semantics, and interaction states are correct
• 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

Semantic Container Selection

Liquid Glass Patterns

// Basic glass effect with fallback
if #available(iOS 26, *) {
    content
        .padding()
        .glassEffect(.regular.interactive(), in: .rect(cornerRadius: 16))
} else {
    content
        .padding()
        .background(.ultraThinMaterial, in: RoundedRectangle(cornerRadius: 16))
}

// Grouped glass elements
GlassEffectContainer(spacing: 24) {
    HStack(spacing: 24) {
        GlassButton1()
        GlassButton2()
    }
}

// Glass buttons
Button("Confirm") { }
    .buttonStyle(.glassProminent)

Review Checklist

State Management

• @State properties are private
• @Binding only where child modifies parent state
• @StateObject for owned, @ObservedObject for injected
• iOS 17+: @State with @Observable, @Bindable for injected
• Passed values NOT declared as @State or @StateObject
• Nested ObservableObject avoided (or passed directly to child views)

Sheets & Navigation (see references/sheet-navigation-patterns.md)

• Using .sheet(item:) for model-based sheets
• Sheets own their actions and dismiss internally

Modern APIs (see references/modern-apis.md)

• Deprecated APIs replaced by current SwiftUI alternatives
• Navigation uses NavigationStack + type-safe destinations where appropriate
• Interaction semantics prefer Button over onTapGesture when possible

Native Semantics & Product Integrity (see references/native-semantic-ui.md)

• Screen-level structure starts from semantic containers before custom stacks
• Edit and display states use different affordances (editable controls vs read-only content)
• Existing user-facing actions are preserved; no fake or placeholder features introduced
• Accessibility identifiers remain unique and intentional
• Icon-only controls have explicit accessibility labels
• UI-focused changes were verified in simulator or previews against real states

ScrollView (see references/scroll-patterns.md)

• Using ScrollViewReader with stable IDs for programmatic scrolling

Text Formatting (see references/text-formatting.md)

• Numeric/date/currency formatting uses modern Text(..., format:) APIs
• User-facing filtering/search uses localized comparisons where appropriate
• Avoiding manual String(format:) for UI text formatting

View Structure (see references/view-structure.md)

• Using modifiers instead of conditionals for state changes
• Complex views extracted to separate subviews
• Container views use @ViewBuilder let content: Content

Performance (see references/performance-patterns.md)

• View body kept simple and pure (no side effects)
• Passing only needed values (not large config objects)
• Eliminating unnecessary dependencies
• State updates check for value changes before assigning
• Hot paths minimize state updates
• No object creation in body
• Heavy computation moved out of body

List Patterns (see references/list-patterns.md)

• ForEach uses stable identity (not .indices)
• Constant number of views per ForEach element
• No inline filtering in ForEach
• No AnyView in list rows

Layout (see references/layout-best-practices.md)

• Avoiding layout thrash (deep hierarchies, excessive GeometryReader)
• Gating frequent geometry updates by thresholds
• Business logic kept in services and models (not in views)
• Action handlers reference methods (not inline logic)
• Using relative layout (not hard-coded constants)
• Views work in any context (context-agnostic)
• safeAreaInset is not being used to fake system-owned keyboard/chrome behavior for UIKit scroll views

Animations (see references/animation-basics.md, references/animation-transitions.md, references/animation-advanced.md)

• Using .animation(_:value:) with value parameter
• Using withAnimation for event-driven animations
• Transitions paired with animations outside conditional structure
• Custom Animatable has explicit animatableData implementation
• Preferring transforms over layout changes for animation performance
• Phase animations for multi-step sequences (iOS 17+)
• Keyframe animations for precise timing (iOS 17+)
• Completion handlers use .transaction(value:) for reexecution

Liquid Glass (iOS 26+)

• #available(iOS 26, *) with fallback for Liquid Glass
• Multiple glass views wrapped in GlassEffectContainer
• .glassEffect() applied after layout/appearance modifiers
• .interactive() only on user-interactable elements
• Shapes and tints consistent across related elements

References

• references/state-management.md - Property wrappers and data flow
• references/view-structure.md - View composition, extraction, and container patterns
• references/performance-patterns.md - Performance optimization techniques and anti-patterns
• references/list-patterns.md - ForEach identity, stability, and list best practices
• references/layout-best-practices.md - Layout patterns, context-agnostic views, and testability
• references/native-semantic-ui.md - Native semantic containers, forms, settings, profile patterns, and screen-by-screen validation guidance
• references/animation-basics.md - Core animation concepts, implicit/explicit animations, timing, performance
• references/animation-transitions.md - Transitions, custom transitions, Animatable protocol
• references/animation-advanced.md - Transactions, phase/keyframe animations (iOS 17+), completion handlers (iOS 17+)
• references/sheet-navigation-patterns.md - Sheet presentation and navigation patterns
• references/scroll-patterns.md - ScrollView patterns and programmatic scrolling
• references/image-optimization.md - AsyncImage, image downsampling, and optimization
• references/liquid-glass.md - iOS 26+ Liquid Glass API
• references/modern-apis.md - Modern SwiftUI API replacements and migration guidance (local extension)
• references/text-formatting.md - Text/number/date formatting and localized matching patterns (local extension)

Philosophy

This skill focuses on facts and best practices, not architectural opinions:

• We don't enforce specific architectures (e.g., MVVM, VIPER)
• We do encourage separating business logic for testability
• We optimize for performance and maintainability
• We follow Apple's Human Interface Guidelines and API design patterns