# SwiftUI on iPhone Duo

> SwiftUI has first-party iPhone Duo support. ArrangementView, ReservedRegion and the vertical toolbar APIs ship in the iOS 27.1 SDK.

Source: https://iphoneduosupport.com/frameworks/swiftui/

Support status: first-party
Apple ships the adaptive APIs directly. Most SwiftUI apps need configuration and layout review rather than rewriting.
Last verified: 2026-09-09

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SwiftUI is the best-supported way to build for iPhone Duo. Declarative layout already recomputes when the available size changes, so a SwiftUI app that avoids fixed sizes gets much of the adaptation for free.

## What you get without changes

Build against the iOS 27.1 SDK and the following already adapt: `NavigationSplitView`, `TabView`, sheets, popovers, context menus, and alerts. Columns collapse when the device is closed and tile or overlay when it is open. Standard navigation and toolbar buttons move into a vertical bar on the inner display in landscape.

## What you need to change

The work concentrates in four places:

1. **Fixed sizes.** Any `.frame(width:)` tuned for a 402-point iPhone is wrong on a 626-point display. See [hard-coded screen dimensions](/checklist/hardcoded-screen-dimensions/).
2. **Orientation logic.** The inner display does not honor supported interface orientations. Move to `@Environment(\.horizontalSizeClass)`. See [size classes](/checklist/size-classes-not-orientation/).
3. **Safe area math.** Insets are asymmetric now. See [asymmetric safe areas](/checklist/asymmetric-safe-area-insets/).
4. **Toolbar content.** A vertical bar holds fewer items. See [overflow priorities](/checklist/toolbar-overflow-priority/).

## The new APIs worth adopting

`ArrangementView` is the highest-value addition — it places a primary and secondary view across every pose, taking size classes, aspect ratio, and active division regions as input:

```swift
ArrangementView {
    PlayerView()
} secondary: {
    UpNextView()
}
.arrangementViewStyle(.split)
```

`ReservedRegion` reports where the hinge divides the display and where the under-display camera occludes it:

```swift
GeometryReader { proxy in
    let regions = proxy.reservedRegions(kind: .division)
}
```

And one modifier that is close to free:

```swift
TabView { … }.defaultTabBarPlacement(.sidebar)
```

Read the full walkthrough in [SwiftUI on iPhone Duo](/blog/swiftui-iphone-duo-adaptive-layout/).

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Published by iPhone Duo Support (https://iphoneduosupport.com). Not affiliated with Apple Inc.