Adaptive layouts around the fold

When iPhone Duo is partially folded the inner display curves through the middle. Anything sitting in that curve gets harder to read and much harder to tap. The same thing happens to a photo printed across the spine of a book: near the gutter it stops reading as one continuous image.

So the fold is not decoration. It is a real constraint on where content can go — and iOS models it as a reserved region you can query and design around.

Reserved regions

Reserved regions are areas of the view that hardware imposes on your layout. Treat them exactly like the window controls you already work around on iPadOS: not obstacles, just facts about the available space.

Two kinds, and the distinction matters:

Division regions split one area into several smaller usable areas. The fold is a division region. Content does not flow through it — it belongs on one side or the other.

Occlusion regions cover part of an area without splitting it. Think of them as frames sitting inside your bounds. The inner FaceTime camera is an occlusion region.

Concretely, iPhone Duo has three reserved regions, and it's worth knowing which is which because they behave differently:

Region	Kind	When it's there
Outer front camera	occlusion	Always. Sits in the corner, aligned with the side controls, and expands into the Dynamic Island for Live Activities.
Inner front camera	occlusion	Only while that camera is active. It's under the display and invisible otherwise; when it activates, UI moves aside to reveal it.
The folding region	division	Only while the device is partially folded, dividing the inner display and excluding the curved centre.

Regions are active or inactive:

• The fold's division region is active only while the device is actually folded. Flat, it is inactive and has zero width.
• The camera's occlusion region is active only while that camera is streaming.

Note the asymmetry between the two cameras: the outer one is a permanent fact of your layout, while the inner one appears and disappears under you. Handle the second as a change you animate through, not a constant you read once.

By default you get only the active ones. Pass the includeInactive option to also see regions that exist but aren't currently in play — which is what you want for stable, high-level decisions. A grid, for instance, can prefer an even column count on any device that has a fold, so the layout doesn't reshuffle every time the user bends the device.

Querying them

In SwiftUI, get a GeometryProxy from GeometryReader or onGeometryChange, then ask it for reservedRegions(kind:), optionally with options: .includeInactive. In UIKit the same method hangs off UIView. Either way you read each region's frame and fold it into your own layout math.

Query reserved regions for custom, manually laid out controls. If you are using system containers, you already have this handled — see below.

Displacement: the design pattern

Most interfaces can simply flow around a reserved region. Some deserve a more deliberate response, and the pattern for that is displacement — adjusting an element's frame based on the available space so that important content stays visible, reachable and unobstructed while the device is folded.

The typical case: an element sits centered while the device is open, and once folded it moves into whichever region actually supports its purpose.

Choose the right scope. Displacement scales from a single button to an entire container. If an element can stand on its own, move it alone. If elements work as a unit, move them together — pulling a context menu away from the photo it belongs to breaks the relationship even though both are technically visible.

Don't move things far. Distance weakens the visual link between an element and its source. Aligning both around the fold usually beats banishing one to the far region.

Don't displace continuously scrolling content. Articles, feeds, documents, lists — these already adapt by scrolling. Relocating them between regions interrupts continuity and gains nothing. Scrollable content is also exempt from fold avoidance generally; it's fine for it to pass under the curve.

Where things should move

Let purpose decide, and note that purpose changes with pose:

• Folded like a book — send transient things such as alerts to the trailing side, near where they will continue to appear as the device closes onto the outer display.
• Propped on a table — the top region is for content that reads at a distance; the bottom region is the stable surface, so tappable controls belong there.
• When several regions would work — pick the contextual one. A focused search field should stay over the view it is searching, adapting its width and position as the device folds, exactly as it stays over the keyboard on iPhone.

How things should adapt once moved

Position and size are the usual changes, but not the only ones. A split view can keep both columns visible by rebalancing to an even 50/50 split. A grid can hold its outer margins and simply widen the gap at the hinge, keeping every cell whole and inside one region.

The through-line: you are moving, resizing and reorganizing what is already there — never removing it. Every piece of content, every function, every layout stays reachable no matter how the device is being held.

Containers that adapt for free

Before writing any of this yourself, check whether a system container already does it:

• Navigation — NavigationStack, NavigationSplitView, TabView
• Content — List, ScrollView
• Presentations — action sheets, alerts, menus, popovers all reposition themselves around reserved regions automatically

Arrangements

Between navigation containers and content containers sits a third kind: a layout container that arranges exactly two views by rule. That's an arrangement, new in iOS 27.1.

The rule is a function. Inputs: horizontal and vertical size class, the view's width-over-height aspect ratio, and whether any division region is currently active. Outputs: whether each view is shown at all, and what frame it gets.

Building one

In SwiftUI, put an ArrangementView inside your NavigationStack and give it a primary and a secondary view. In UIKit, use UIArrangementViewController as the root of a UINavigationController and assign view controllers to the .primary and .secondary placements.

The split style

The default. It divides the bounds between the two views — horizontally when the view is wider than tall, vertically when taller than wide.

Constrain it when only one axis makes sense: apply .axes(.horizontal) to the split style (in UIKit, configure UISplitArrangement the same way and pass it to updateArrangement(_:)). When a split arrangement can't split along the view's primary axis, it shows a single view rather than producing a bad layout.

The payoff on this device: when the secondary view is dismissed, the primary doesn't recenter across the whole display the way it would on iPad. It stays inside the region the fold defines, so its controls stay reachable and clear of the curve.

The overlay style

Where split prefers side-by-side, overlay prefers stacking one view above the other — and moves them side-by-side when the device folds, which is exactly when the stacked view would otherwise get cramped.

Because the relationship changes with the pose, you often want to change the subordinate view's presentation to match. Read the stacking state and adapt: in SwiftUI, the overlayArrangementZIndex environment value; in UIKit, state(for:) on the arrangement view controller and then its zIndex. A list that is collapsed while stacked can expand once it's given its own region.

Choosing between them

Follow the pattern the app already uses. Something built from HStack/VStack maps to split; something built from ZStack maps to overlay. Both translate directly and bring iPhone Duo support with them.

With no existing pattern to follow, ask what the relationship between the two views is:

• Foreground over background, where partial obscuring is acceptable — overlay. Controls floating over readable content that scrolls beneath them is the canonical case.
• Main and detail, where neither may ever be obscured — split. A player and its transcript is the canonical case.

When not to use one

• Arrangements provide no navigation infrastructure. Don't put a NavigationSplitView or similar inside one.
• Don't nest an arrangement inside List or ScrollView.
• If you need expanding and collapsing column behavior, you want a real split view, not an arrangement.

A working order

1. Audit centered layouts. Would a two-column layout be better? If not, which displacement pattern applies?
2. Prefer system containers and presentations — most adaptation is free.
3. Where the app has a custom horizontal split or overlay, replace it with ArrangementView. You gain iPhone Duo behavior across every supported device, not just this one.
4. Only then, for the highest-priority manually positioned controls, adopt the reserved-region APIs and implement displacement by hand.

For hinge-driven interaction rather than layout, see ../iphone-duo-hinge-and-scenes/SKILL.md — live hinge angle is the wrong tool for laying out views, and the right one for driving effects.