Building adaptive layouts for iPhone Duo with ArrangementView

The new container: ArrangementView

In SwiftUI, the primary tool for adaptive layouts on iPhone Duo is ArrangementView, a new container introduced with the iOS 27.1 SDK. UIKit developers get the equivalent as UIArrangementViewController. Both manage primary and secondary content areas and automatically adjust them based on the fold and any reserved regions the system defines, rather than requiring you to branch your layout code on device state.

This matters because iPhone Duo has two genuinely different displays — a 5.4-inch outer display and a 7.6-inch inner display — plus a Split View mode on the inner display that divides it into two fixed panes. A layout system built around explicit device checks would need to handle every combination separately. ArrangementView is designed to absorb that complexity for you.

Reserved regions instead of hardcoded coordinates

The second piece of the puzzle is ReservedRegion, exposed through GeometryProxy.reservedRegions(kind:) in SwiftUI and UIViewReservedRegion in UIKit. These let you query hardware-specific areas — such as the fold itself or a camera occlusion — by kind, for example .division or .occlusion, rather than hardcoding pixel coordinates that would break the moment Apple ships a second-generation device with a different hinge geometry.

What Apple explicitly warns against

According to Apple's guidance, you should avoid hardcoding layouts based on orientation or a reference to the main screen. Concretely, that means retiring patterns like checking UIScreen.main directly and branching logic on portrait versus landscape as a proxy for fold state. Instead, the guidance points developers toward size classes and dynamic scene geometry queried at runtime.

Where this leaves existing apps

If your app already uses size classes and standard system containers like NavigationSplitView, you are closer to compliant than you might think — the underlying pattern iOS has pushed for years turns out to be exactly what iPhone Duo needs. If your app hardcodes screen dimensions or checks device idiom directly, that is the part worth prioritizing first.

For the broader picture of why this matters to end users, see our explainer on why some apps still show black bars in Split View — that visible symptom is exactly what happens when an app has not yet adopted ArrangementView and reserved regions. And if you are setting up your development environment for this work, start with our guide to iOS 27, Xcode 27.1 beta, and macOS Tahoe 26.6.