Swiftui Expert Skill

SwiftUI Expert Skill

Operating Rules

• Consult references/latest-apis.md at the start of every task to avoid deprecated APIs
• Only adopt Liquid Glass when explicitly requested by the user (use the swiftui-liquid-glass skill)
• Use #available gating with sensible fallbacks for version-specific APIs

SwiftUI Code Workflow

Review existing SwiftUI code

• Read the code under review and identify which topics apply
• Flag deprecated APIs (compare against references/latest-apis.md)
• Run the Topic Router below for each relevant topic
• Validate #available gating and fallback paths for iOS 26+ features

Improve existing SwiftUI code

• Audit current implementation against the Topic Router topics
• Replace deprecated APIs with modern equivalents from references/latest-apis.md
• Refactor hot paths to reduce unnecessary state updates
• Extract complex view bodies into separate subviews
• Suggest image downsampling when UIImage(data:) is encountered (optional optimization, see references/image-optimization.md)

Implement new SwiftUI feature

• Design data flow first: identify owned vs injected state
• Structure views for optimal diffing (extract subviews early)
• Apply correct animation patterns (implicit vs explicit, transitions)
• Use Button for all tappable elements; add accessibility grouping and labels
• Gate version-specific APIs with #available and provide fallbacks

Instruments Trace Workflow

Record a new Instruments trace

Trigger when the user asks to "record a trace", "profile the app", "capture a session", etc. Full reference: references/trace-recording.md.

1. Confirm target — attach to a running app, launch an app, or record all processes? If the user didn't say, ask. List connected devices when useful:

``bash python3 "${SKILL_DIR}/scripts/record_trace.py" --list-devices ``

1. Pick a template based on target kind — the SwiftUI template populates the SwiftUI lane on any real device: a physical iOS/iPadOS device or the host Mac. The only exception is the iOS Simulator, where the SwiftUI lane comes back empty — switch to --template "Time Profiler" in that case (still gives Time Profiler + Hangs + Animation Hitches). Always check --list-devices: simulators kind → Time Profiler; devices kind (real devices and the host Mac) → default SwiftUI. Full decision table in references/trace-recording.md.
2. Start the recording. For agent-driven sessions where the user says "I'll tell you when I'm done", start in the background and use a stop-file:

``bash python3 "${SKILL_DIR}/scripts/record_trace.py" \ --device "" --attach "" \ --stop-file /tmp/stop-trace --output ~/Desktop/session.trace `` For interactive sessions, just tell the user to press Ctrl+C when done.

1. Signal stop — when the user says they've finished exercising the app, touch /tmp/stop-trace. The script cleanly SIGINTs xctrace and waits up to 60s for finalisation.
2. Analyse the resulting trace (flow into the "Trace-driven improvement" workflow below).

Trace-driven improvement (Instruments .trace provided)

Trigger whenever the user's request references a .trace file. A target SwiftUI source file is optional — if given, cite specific lines; if not, recommend where to look based on view names and symbols the trace already reveals.

Full reference: references/trace-analysis.md. Summary of the composition pattern:

1. Scope the analysis. Ask yourself: does the user want the whole trace, or a slice?

• "focus on X / after X / between X and Y / during X" → resolve to a window first (see step 2).
• No scoping cue → analyse the whole trace.

1. Resolve a window (only if the user scoped). The parser exposes two discovery modes:

``bash # Find a log that marks the start/end of the region of interest: python3 "${SKILL_DIR}/scripts/analyze_trace.py" --trace \ --list-logs --log-message-contains "loaded feed" --log-limit 5 # Or list os_signpost intervals (paired begin/end), filterable by name: python3 "${SKILL_DIR}/scripts/analyze_trace.py" --trace \ --list-signposts --signpost-name-contains "ImageDecode" ` Both modes accept --window STARTMS:ENDMS to scope discovery. Pick the timems (for logs) or startms/end_ms (for signposts) that match the user's description. Build a window like --window 10400:11700`.

1. Run the main analysis (with or without --window):

``bash python3 "${SKILL_DIR}/scripts/analyze_trace.py" --trace \ --json-only --top 10 [--window START_MS:END_MS] ``

1. Interpret with references/trace-analysis.md — key diagnostics:

• main_running_coverage_pct inside each correlation ("` to get the ranked list of source nodes driving the updates.

1. Optionally ground in source. If the user pointed at a file, read it and match view names / user-code symbols against identifiers there. If not, recommend which files to open based on the view names SwiftUI reported.
2. Return a prioritised plan. Cite evidence (coverage %, hot symbol, overlapping view, log timestamp, cause-graph edges) and route each recommendation to a Topic Router reference.
3. Only edit code if the user asked for edits.

Topic Router

Consult the reference file for each topic relevant to the current task:

| Topic | When it applies | Reference | |-------|-----------|-----------| | State management | Property wrapper choice, data flow design | references/state-management.md | | View composition | Extracting subviews, container patterns | references/view-structure.md | | Performance | Diagnosing hangs, hitches, excessive updates | Use the swiftui-performance-audit skill | | Lists and ForEach | List rendering, identity, filtering | references/list-patterns.md | | Layout | GeometryReader alternatives, layout containers | references/layout-best-practices.md | | Sheets and navigation | Sheets, NavigationSplitView, Inspector | references/sheet-navigation-patterns.md | | ScrollView | Programmatic scrolling, ScrollViewReader | references/scroll-patterns.md | | Focus management | @FocusState, focusable views | references/focus-patterns.md | | Animations (basics) | Implicit/explicit animations, timing | references/animation-basics.md | | Animations (transitions) | View transitions, matchedGeometryEffect | references/animation-transitions.md | | Animations (advanced) | Phase/keyframe animations, @Animatable | references/animation-advanced.md | | Accessibility | VoiceOver, Dynamic Type, grouping, traits | references/accessibility-patterns.md | | Swift Charts | Chart marks, axes, selection, styling | references/charts.md | | Charts accessibility | Charts VoiceOver, Audio Graph | references/charts-accessibility.md | | Image optimization | AsyncImage, downsampling, caching | references/image-optimization.md | | Liquid Glass (iOS 26+) | Adopting or reviewing Liquid Glass | Use the swiftui-liquid-glass skill | | macOS scenes | Settings, MenuBarExtra, multi-window | references/macos-scenes.md | | macOS window styling | Toolbar styles, window sizing, Commands | references/macos-window-styling.md | | macOS views | HSplitView, Table, AppKit interop | references/macos-views.md | | Text patterns | Text initializer choice, localization | references/text-patterns.md | | Deprecated API lookup | Checking if an API is deprecated | references/latest-apis.md | | Instruments trace analysis | Given a .trace file to interpret | references/trace-analysis.md | | Instruments trace recording | Asked to record a new trace | references/trace-recording.md |

Correctness Checklist

These are hard rules -- violations are always bugs:

• [ ] @State properties are private
• [ ] @Binding only where a child modifies parent state
• [ ] Passed values never declared as @State or @StateObject (they ignore updates)
• [ ] @StateObject for view-owned objects; @ObservedObject for injected
• [ ] iOS 17+: @State with @Observable; @Bindable for injected observables needing bindings
• [ ] ForEach uses stable identity (never .indices for dynamic content)
• [ ] Constant number of views per ForEach element
• [ ] .animation(_:value:) always includes the value parameter
• [ ] @FocusState properties are private
• [ ] No redundant @FocusState writes inside tap gesture handlers on .focusable() views
• [ ] iOS 26+ APIs gated with #available and fallback provided
• [ ] import Charts present in files using chart types

References

• references/latest-apis.md -- Read first for every task. Deprecated-to-modern API transitions (iOS 15+ through iOS 26+)
• references/state-management.md -- Property wrappers, data flow, @Observable migration
• references/view-structure.md -- View extraction, container patterns, @ViewBuilder (for reordering/refactoring an existing view file's structure, DI, and Observation usage, use the swiftui-view-refactor skill instead)
• references/list-patterns.md -- ForEach identity, Table (iOS 16+), inline filtering pitfalls
• references/layout-best-practices.md -- Layout patterns, GeometryReader alternatives
• references/accessibility-patterns.md -- VoiceOver, Dynamic Type, grouping, traits
• references/animation-basics.md -- Implicit/explicit animations, timing, performance
• references/animation-transitions.md -- View transitions, matchedGeometryEffect, Animatable
• references/animation-advanced.md -- Phase/keyframe animations (iOS 17+), @Animatable macro (iOS 26+)
• references/charts.md -- Swift Charts marks, axes, selection, styling, Chart3D (iOS 26+)
• references/charts-accessibility.md -- Charts VoiceOver, Audio Graph, fallback strategies
• references/sheet-navigation-patterns.md -- Sheets, NavigationSplitView, Inspector
• references/scroll-patterns.md -- ScrollViewReader, programmatic scrolling
• references/focus-patterns.md -- Focus state, focusable views, focused values, default focus, common pitfalls
• references/image-optimization.md -- AsyncImage, downsampling, caching
• references/macos-scenes.md -- Settings, MenuBarExtra, WindowGroup, multi-window
• references/macos-window-styling.md -- Toolbar styles, window sizing, Commands
• references/macos-views.md -- HSplitView, Table, PasteButton, AppKit interop
• references/text-patterns.md -- Text initializer selection, verbatim vs localized
• references/trace-analysis.md -- Parse Instruments .trace files via scripts/analyze_trace.py; interpret main-thread coverage, high-severity SwiftUI updates, hitch narratives, and map findings back to source files
• references/trace-recording.md -- Record a new trace via scripts/record_trace.py: attach to a running app, launch one fresh, or capture a manually-stopped session; supports stop-file for agent-driven flows

Source: AvdLee/SwiftUI-Agent-Skill, adapted.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: patrickserrano
• Source: patrickserrano/lacquer
• License: MIT
• Homepage: https://patrickserrano.github.io/lacquer/

Install and usage instructions live in the source repository linked above.