UIKit Modernization

Guidance for the scene-based life cycle and resizability changes that UIKit requires in the iOS 27 cycle — the highest-impact UIKit change in years, because it gates whether your app launches at all.

When to Use

Use this skill when:

• Building against the iOS 27 SDK and your app uses only a UIApplicationDelegate (no scene delegate)
• Your app "won't launch" after updating to the latest SDK
• Making an iPhone app adapt to arbitrary window sizes (iPhone Mirroring on Mac, iPhone apps on iPad)
• Adapting your resizing baseline for iPhone Duo, Apple's two-display foldable iPhone
• Replacing UIScreen.main, interface idiom, or orientation checks with adaptive equivalents
• Adopting iOS 27 additive APIs — tab bar sidebar/prominent tab, nav bar minimization, menu image visibility, CoreMotion/CoreLocation Body protocols
• Fixing behavior that breaks in iPhone Mirroring — dead custom gestures, failing Face ID prompts, layouts stuck in portrait
• Adding a navigation bar subtitle (subtitle, largeSubtitleView) or styling one with attributed strings (iOS 26)
• Adding pointer effects (UIPointerInteraction) or hardware-keyboard commands (UIKeyCommand, the hold-⌘ HUD) to a UIKit app
• Planning a UIKit → scene-lifecycle migration

Example Prompts

• "My UIKit app won't launch on iOS 27"
• "How do I adopt the scene-based life cycle?"
• "What replaces UIScreen.main?"
• "How do I make my iPhone app resizable?"
• "How do I set a minimum window size or lock orientation on iOS 27?"
• "Should I use the interface idiom or size classes for layout?"
• "How do I put a tab bar in a sidebar on iPhone? (iOS 27)"
• "My custom pinch gesture stops working in iPhone Mirroring"
• "Why does Face ID fail when my app runs through iPhone Mirroring?"
• "My UIKeyCommand doesn't show in the iPad hold-Command HUD"
• "How do I put a filter button under my large title with largeSubtitleView?"
• "Why does largeSubtitleTextAttributes have no effect?"
• "What goes in UIApplicationSceneManifest for a single-window app?"
• "What should I clean up in sceneDidDisconnect?"
• "How do I open a new window from UIKit code?"
• "How do I let users drag an item out to open it as a new window on iPad?"
• "Cmd-Z in one window undoes edits made in another window"
• "How do I disable Scribble on one text field?"
• "Why was my upload rejected for a missing launch screen?"
• "What's the View Annotations API for Siri?"

What This Skill Provides

• The scene-lifecycle requirement at iOS 27 (apps without a UISceneDelegate no longer launch) and the migration path
• Info.plist configuration – the UIApplicationSceneManifest structure, the launch-screen key validated at upload on the 27 SDK (TN3208), and destinations-vs-device-checks
• Scene lifecycle edges – sceneDidDisconnect teardown semantics, UISceneSessionActivationRequest window opening, drag-to-create-window (drag items carrying an NSUserActivity, gated on NSUserActivityTypes), per-window undo scoping, per-scene NSUserActivity restoration, external-display scene roles, and the displayGamut/legibilityWeight/activeAppearance traits
• A don't/do table for replacing UIScreen.main, screen.scale, screen.bounds, idiom, and orientation with scene/trait/size-class equivalents
• The new iOS 27 additive APIs — prominentTabIdentifier, UITabBarControllerSidebar.preferredPlacement, navigationBarMinimization, UIMenuElement.preferredImageVisibility, deviceMotionBody/headingBody
• iPhone Mirroring compatibility – the always-portrait orientation trap, indirect trackpad/mouse input reaching custom gesture recognizers (UIApplicationSupportsIndirectInputEvents, scroll-type masks), companion Face ID approval on the Mac (iOS 18), and cross-device drag and drop
• Desktop-class input – UIPointerInteraction pointer effects, UIHoverGestureRecognizer, UIKeyCommand with discoverabilityTitle for the hold-⌘ shortcut HUD, and Scribble (UIScribbleInteraction / UIIndirectScribbleInteraction) for Pencil handwriting
• Navigation bar titles and subtitles (iOS 26) – attributedTitle, subtitle, attributedSubtitle, subtitleView, and the large-title slots (largeTitle, largeSubtitle, largeAttributedSubtitle, largeSubtitleView), which property wins, the two-line titleView fallback for apps that keep UIDesignRequiresCompatibility (where subtitles don't render), and behavior verified on iOS 26.5 and 27 (ignored largeSubtitleTextAttributes, largeSubtitleView hidden when the title collapses, empty custom views hiding the text subtitle)
• Apple Intelligence touchpoints (menu "Ask Siri", View Annotations, drag-and-drop resource loading)
• How to let Xcode 27's app-modernization agent do the mechanical rewrites

Related

• UIKit-SwiftUI Bridging – embedding SwiftUI in a modernized scene-based UIKit app
• App Composition – app-level integration and UIKit → SwiftUI migration priority
• SwiftUI Layout – size-class-driven adaptive layout, the recommended replacement for idiom/orientation checks
• iPhone Duo – the two-display device that builds on this resizing baseline
• SwiftUI Toolbars – the SwiftUI side of navigation subtitles (navigationSubtitle and the .largeSubtitle placement), for SwiftUI screens in the same app