UIKit & Bridging

You MUST use this skill for ANY UIKit bridging, Auto Layout, Combine, TextKit, or UIKit animation work.

Can't launch Axiom agents? Where this router sends you to an agent, follow its procedure inline. Over MCP, axiom_get_agent returns it; elsewhere, read its file below, which needs only file search and read.

Available here: skills/resize-auditor.md.

For any other agent, over MCP axiom_get_agent returns it too; run its xclog, xcsym and xcprof steps with the axiom_xclog_*, axiom_xcsym_* and axiom_xcprof_* tools. Elsewhere, search Axiom's skills for skills/<agent>.md; if there is none, do that work yourself with this suite's skills, using any Axiom tool on your PATH.

Quick Reference

Symptom / Task	Reference
UIViewRepresentable, UIViewControllerRepresentable	See skills/uikit-bridging.md
Embedding SwiftUI in UIKit (UIHostingController)	See skills/uikit-bridging.md
Coordinator pattern, updateUIView lifecycle	See skills/uikit-bridging.md
Building adaptive UIKit layout: guides, width-conditional constraints, compositional layout, self-sizing cells	See skills/adaptive-layout.md
"Unable to simultaneously satisfy constraints"	See skills/auto-layout-debugging.md
Constraint conflicts, ambiguous layout	See skills/auto-layout-debugging.md
Views not appearing, positioned incorrectly	See skills/auto-layout-debugging.md
CAAnimation completion handler not firing	See skills/uikit-animation-debugging.md
Spring physics wrong on device, duration mismatch	See skills/uikit-animation-debugging.md
Animation jank, CATransaction timing	See skills/uikit-animation-debugging.md
Combine publishers, AnyCancellable lifecycle	See skills/combine-patterns.md
@Published properties, Combine ↔ async/await	See skills/combine-patterns.md
When to use Combine vs async/await	See skills/combine-patterns.md
UIScene lifecycle required, resizable apps, size classes, tab sidebar OS27	See skills/uikit-modernization.md
iPhone Mirroring compat: indirect input, companion Face ID, portrait trap	See skills/uikit-modernization.md
Scene edges: teardown, activation requests, per-scene restoration, external display, activeAppearance	See skills/uikit-modernization.md
Nav bar title and subtitle: UINavigationItem.subtitle, largeSubtitleView, attributedTitle/attributedSubtitle, subtitle text attributes (iOS 26)	See skills/uikit-modernization.md
Automated resize-readiness scan (scene lifecycle, UIScreen.main, fixed-canvas, Mirroring input, iPhone Duo)	Launch resize-auditor agent or /axiom:audit resize
iPhone Duo in UIKit: vertical bars, the fold, window requests on the outer display	See axiom-swiftui (skills/iphone-duo.md) — UIKit equivalents sit beside each SwiftUI API
TextKit 2 architecture, NSTextLayoutManager	See skills/textkit-ref.md
Writing Tools integration (iOS 26)	See skills/textkit-ref.md
Viewport rendering surfaces, attachment reuse, collapsible text OS27	See skills/textkit-ref.md
SwiftUI TextEditor, TextKit 1 migration	See skills/textkit-ref.md
Grammar checking (UITextChecker), per-edge text-block borders OS27	See skills/textkit-ref.md
PencilKit canvas, PKToolPicker, drawing persistence	See skills/pencilkit-paperkit.md
Apple Pencil Pro (squeeze, barrel roll, hover, haptics)	See skills/pencilkit-paperkit.md
Handwriting recognition (PKStrokeRecognizer), stroke identity/slicing OS27	See skills/pencilkit-paperkit-ref.md
PaperKit markup canvas (shapes, images, text + drawing)	See skills/pencilkit-paperkit-ref.md
PaperKit programmatic markup model (subelements, adornments) OS27	See skills/pencilkit-paperkit-ref.md

Decision Tree

digraph uikit {
    start [label="UIKit task" shape=ellipse];
    what [label="What do you need?" shape=diamond];

    start -> what;
    what -> "skills/uikit-bridging.md" [label="wrap UIKit in SwiftUI\nor SwiftUI in UIKit"];
    what -> "skills/adaptive-layout.md" [label="build adaptive layout\n(guides, constraint sets,\ncompositional)"];
    what -> "skills/auto-layout-debugging.md" [label="constraint errors,\nlayout issues"];
    what -> "skills/uikit-animation-debugging.md" [label="CAAnimation bugs,\nspring physics,\ncompletion handlers"];
    what -> "skills/combine-patterns.md" [label="publishers, sinks,\n@Published,\nasync/await bridge"];
    what -> "skills/textkit-ref.md" [label="text layout,\nWriting Tools,\nTextKit migration"];
    what -> "skills/pencilkit-paperkit.md" [label="drawing canvas,\nApple Pencil,\nPaperKit markup"];
    what -> "skills/uikit-modernization.md" [label="scene lifecycle (required 27),\nresizable apps,\nsize classes"];
}

1. Scene-lifecycle migration, "app won't launch on 27", resizability, size classes, tab sidebar? → skills/uikit-modernization.md 0b. App misbehaves in iPhone Mirroring (gestures dead, Face ID blocked, layout stuck portrait)? → skills/uikit-modernization.md 0c. iPhone Duo / foldable iPhone (vertical bars, the fold, outer-display window requests)? → axiom-swiftui (skills/iphone-duo.md)
2. UIViewRepresentable / UIViewControllerRepresentable / UIHostingController? → skills/uikit-bridging.md
3. "Unable to simultaneously satisfy constraints" / layout bugs? → skills/auto-layout-debugging.md 2b. Building a layout that adapts (layout guides, size-class constraint sets, compositional column math, self-sizing cells)? → skills/adaptive-layout.md
4. CAAnimation completion missing / spring physics wrong / animation jank? → skills/uikit-animation-debugging.md
5. Combine publishers / AnyCancellable / @Published / Combine ↔ async bridge? → skills/combine-patterns.md
6. TextKit 2 / Writing Tools / TextEditor / TextKit 1 migration? → skills/textkit-ref.md
7. PencilKit canvas / Apple Pencil / PaperKit markup? → skills/pencilkit-paperkit.md
8. Pure SwiftUI view question (no UIKit bridging)? → /skill axiom-swiftui
9. Design decisions, HIG, Liquid Glass, SF Symbols, typography? → /skill axiom-design
10. Block retain cycles in UIKit callbacks? → See axiom-performance (skills/objc-block-retain-cycles.md)
11. Memory leaks from Combine subscriptions? → Start with skills/combine-patterns.md, then axiom-performance if leak persists

Conflict Resolution

uikit vs swiftui: When working with UI code:

• Use uikit when wrapping UIKit in SwiftUI or vice versa, or debugging UIKit-specific issues (Auto Layout, CAAnimation)
• Use swiftui for pure SwiftUI views, navigation, layout, animations

uikit vs concurrency: When Combine interacts with async/await:

• Use uikit (skills/combine-patterns.md) for bridging Combine pipelines with async/await
• Use concurrency for pure async/await patterns, actors, Sendable

uikit vs performance: When animations or layout cause performance issues:

1. Try uikit FIRST — Most animation jank is CATransaction timing or layer state, not a profiling issue
2. Only use performance if animation logic is correct but rendering is slow

uikit vs axiom-data: When @Published properties relate to data persistence:

• Use uikit for Combine publisher patterns and @Published lifecycle
• Use axiom-data for SwiftData/Core Data model layer concerns

Anti-Rationalization

Thought	Reality
"I'll just use UIHostingController, it's simple"	Hosting has sizing, lifecycle, and navigation edge cases. skills/uikit-bridging.md covers the gotchas.
"Auto Layout error is just a warning, I'll ignore it"	Unsatisfied constraints cause unpredictable layout at runtime. Fix them now.
"I know how CAAnimation works"	90% of CAAnimation bugs are CATransaction timing, not Core Animation. Check skills/uikit-animation-debugging.md.
"Combine is dead, just rewrite with async/await"	Combine has no deprecation notice. Rewriting working pipelines wastes time. skills/combine-patterns.md covers when to migrate vs maintain.
"TextKit 1 still works fine"	TextKit 1 misses Writing Tools integration and has known layout bugs Apple won't fix. See skills/textkit-ref.md.
"I'll store cancellables in a local variable"	Local AnyCancellable deallocates immediately, killing the subscription.
"I'll archive the PKCanvasView to save the drawing"	Archiving the view loses editability. Persist drawing.dataRepresentation(). See skills/pencilkit-paperkit.md.
"My tool picker won't show, the API must be broken"	The canvas must becomeFirstResponder() after setVisible(_:forFirstResponder:). See skills/pencilkit-paperkit.md.

Example Invocations

User: "How do I wrap a UIKit view in SwiftUI?" → Read: skills/uikit-bridging.md

User: "I'm getting 'Unable to simultaneously satisfy constraints'" → Read: skills/auto-layout-debugging.md

User: "My CAAnimation completion handler never fires"