UIScreen.main on iPhone Duo — What to Use Instead

Why it breaks

Do not use UIScreen.main on a two-display device: iPhone Duo has an inner display and an outer display, and your app can share a display in Split View, so "the main screen" is not the window you are drawing into and not the size of your scene. Apple has said UIScreen.main is heading for deprecation.

The inner display does not honor supported interface orientations — it rotates regardless of your Info.plist mask. That means interfaceOrientation, UIDevice.current.orientation, and statusBarOrientation will lie about the layout you should use. The same trap applies to userInterfaceIdiom and device-model checks: they describe hardware, not the Compact or Regular width of the current scene.

Existing iPhone apps usually fail here in three places: a launch splash or overlay sized to UIScreen.main.bounds, a landscape branch that never fires on the inner display, and a Compact-only stack that never expands when Duo unfolds. For SwiftUI patterns after the swap, see the SwiftUI guide. For fold chrome, see ReservedRegion. For split / overlay placement, see ArrangementView.

UIScreen.main replacements

Size layout to the view or scene you own — never UIScreen.main.bounds. When you truly need a UIScreen, take it from the current window scene, as in Apple's Tech Talk Prepare your app for iPhone Duo.

let screen = window?.windowScene?.screen

let screen = view.window?.windowScene?.screen

• Layout size: the view's bounds, the scene's bounds, GeometryReader / containerRelativeFrame, or SwiftUI environment geometry.
• Scale: traitCollection.displayScale instead of UIScreen.main.scale.
• A real UIScreen object only when you need that display — for example displayScale on a specific screen, or coordinating with an outer-display scene. Copy the one-liners above; never UIScreen.main.

// Before — hardware display, not your window
let width = UIScreen.main.bounds.width
overlay.frame = CGRect(x: 0, y: 0, width: width, height: 44)

let scale = UIScreen.main.scale
snapshot.scale = scale

// After — the view you actually own
override func viewDidLayoutSubviews() {
    super.viewDidLayoutSubviews()
    overlay.frame = CGRect(
        x: 0,
        y: 0,
        width: view.bounds.width,
        height: 44
    )
}

let scale = traitCollection.displayScale
snapshot.scale = scale

// SwiftUI: measure the container, not the display
GeometryReader { proxy in
    Banner()
        .frame(width: proxy.size.width)
}

Content()
    .containerRelativeFrame(.horizontal) { width, _ in width }

Orientation replacements

On Duo's inner display the system does not honor supported interface orientations — drive layout from size classes, not from Info.plist masks, interfaceOrientation, or UIDevice orientation.

Do not branch on landscape vs portrait, and do not treat .phone as Compact. In UIKit, read traitCollection.horizontalSizeClass and register for trait changes. In SwiftUI, read the environment values Apple cites in the same Tech Talk:

@Environment(\.horizontalSizeClass)
private var horizontalSizeClass

@Environment(\.verticalSizeClass)
private var verticalSizeClass

// Before — these lie on Duo's inner display
if UIDevice.current.orientation.isLandscape {
    useWideLayout()
}
if UIApplication.shared.statusBarOrientation.isLandscape {
    useWideLayout()
}
if windowScene.interfaceOrientation.isLandscape {
    useWideLayout()
}
if traitCollection.userInterfaceIdiom == .phone {
    useCompactLayout()
}

// After — available width, not rotation or device identity
func applyLayout(for sizeClass: UIUserInterfaceSizeClass) {
    if sizeClass == .regular {
        useWideLayout()
    } else {
        useCompactLayout()
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    applyLayout(for: traitCollection.horizontalSizeClass)
    registerForTraitChanges(
        [UITraitHorizontalSizeClass.self]
    ) { (view: Self, _) in
        view.applyLayout(for: view.traitCollection.horizontalSizeClass)
    }
}

var body: some View {
    if horizontalSizeClass == .regular {
        TwoColumnLayout()
    } else {
        SingleColumnLayout()
    }
}

Grep checklist

Search the project — including storyboards, launch screens, and third-party UI kits — for every call site, then re-test in the Duo Simulator. The Xcode testing guide covers Device Hub poses; the compatibility checklist is the shipping gate for this item.

• UIScreen.main — including .bounds, .scale, .nativeBounds, and coordinate-space helpers
• UIDevice.current.orientation
• statusBarOrientation
• interfaceOrientation

After the grep is clean, fold, unfold, rotate the inner display, and resize Split View. If a view still assumes a full-screen rectangle, it was reading the wrong bounds even if it never named UIScreen.

Frequently asked questions