Modernize your UIKit app

Key Takeaways

• Make your app resize to any scene size

• Adopt scene lifecycle and drop UIScreen.main

• Replace idiom/orientation checks with size classes

• Consider new bar and menu APIs

Presenters

• Michael Ochs, UI Frameworks Engineering Manager

Changes to app adaptivity requirements

• iOS 27: apps must dynamically adjust to any scene size at runtime

  • iPhone Mirroring on the Mac lets people fully resize the iPhone window

  • an iPhone-only app on iPad is fully resizable like any other iPad app

1. Adopt scene lifecycle

• Scene lifecycle is required when building with the latest SDKs, and without it the app no longer launches

• Use a UISceneDelegate, the basis for any adaptive app

2. Stop referencing the main screen

• The scene’s screen can change (mirroring, external display), so UIScreen.main gives wrong info

• Read the screen from the window’s scene instead, and get available space from the view or the scene’s effectiveGeometry

// Access the screen through the windowScene, not UIScreen.main
let screen = window?.windowScene?.screen

• Get available space from the view (view.bounds) or the scene’s effectiveGeometry, not the screen

• Prefer traitCollection.displayScale over the screen’s scale

// Replace the screen's scale with trait collection's displayScale
override func layoutSubviews() {
    super.layoutSubviews()

    // layoutSubviews will be called again automatically when displayScale changes
    let displayScale = traitCollection.displayScale
    // ...
}

• Traits are auto-tracked in common methods (layoutSubviews, updateProperties, draw(_:)), and for other cases you observe changes with registerForTraitChanges

let displayScaleTrait: [UITrait] = [UITraitDisplayScale.self]
registerForTraitChanges(displayScaleTrait) {
    (view: GalleryView, previousTraitCollection: UITraitCollection) in
    view.cache.invalidate()
}

3. Stop checking idiom and orientation for layout

• Use size classes for sizing decisions instead of the user interface idiom (an iPhone app on iPad or in mirroring still runs under the phone idiom)

• Supported interface orientations are only a preference and are ignored in a resizable environment, so do not base layout on interface orientation

  • iPhone Mirroring on the Mac always runs in portrait

• Games: UIRequiresFullScreen is honored on iPhone from iOS 27, but now enables discrete resizing (snapping to configurations that match supported orientations) instead of fully opting out

New APIs: Bars and Menus

Tab bar

• On iPad, a tab bar can expand into a full sidebar representation

• On iPhone, the bottom tab bar is shown across all sizes by default

• New in iOS 27: an iPhone app can also opt into a sidebar

  • it is an app choice, and the system shows it only when there is room (e.g. a regular horizontal size class), with no UI toggle

  • check sidebar.isAvailable, and when it is not, surface that UI behind nested tabs elsewhere

// Opt into the sidebar representation
tabBarController.sidebar.preferredPlacement = .sidebar

// Is a sidebar currently available?
tabBarController.sidebar.isAvailable

• Highlight a key tab with prominentTabIdentifier, which stays visible even when the tab bar collapses during scrolling

let tabs = [
    // ...
]

let tabBarController = UITabBarController(tabs: tabs)
tabBarController.prominentTabIdentifier = "cart"

Navigation bar

• Navigation bars can interactively slide away as people scroll, giving content more room

• Customize the minimization behavior

  • navigationItem.barMinimizationBehavior = .always

  • set navigationItem.barMinimizationSafeAreaAdjustment = .never if you handle safe area avoidance yourself, so insets are not adjusted automatically

• The .automatic scroll edge effect now provides its own visuals instead of switching between soft and hard, so re-evaluate any previous override (especially .soft)

Menu image

• With Liquid Glass, images on menu elements may not show by default in some contexts (e.g. iPadOS and macOS)

• Set preferredImageVisibility to override the default and keep an image visible

Supports Apple Intelligence

• iOS 27 menus gain an Ask Siri button, an entry point to start a conversation with Siri from your app

  • menus show it automatically when there is content relevant for Siri

• Give Siri app-specific context with the new View Annotations API, annotating specific views with AppEntity values

  • Learn more: Explore advanced App Intents features for Siri and Apple Intelligence

• If your app supports drag and drop, Siri can load resources through your existing drag handlers

  • when invoked from a context menu, the system calls your drag delegate methods to load the content

  • a drag session can start without a user gesture, so avoid animations or modal UI in sessionWillBegin

  • if you show stateful UI when a drag begins, put that code in sessionDidMove instead