Place a sheet on one side with presentationPlacement on iPhone Duo

On a regular iPhone, a sheet fills the width of the screen, so there is nothing to place. On an open iPhone Duo, the screen is wide, and a sheet only takes part of it.

iOS 27 lets you choose which side that sheet sits on:

• SwiftUI: presentationPlacement(_:)
• UIKit: UISheetPresentationController.preferredPlacement

How to use presentationPlacement

Like the other presentation modifiers, it goes on the content of the sheet, not on the view that presents it.

.sheet(isPresented: $showNewList) {
    NewListView()
        .presentationPlacement(.trailing)
}

There are four placements:

.leading, .center, and .trailing are iOS only. On macOS, tvOS, watchOS, and visionOS, you only get .automatic.

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Fully open

This is where the placement shows the most.

With .automatic, the sheet sits in the middle, with the app visible on both sides. .center looks the same.

.leading moves the sheet to the leading edge, the left edge in a left-to-right language.

.trailing moves it to the trailing edge, on the right. That edge is where iPhone Duo puts its vertical bar, so the sheet's Close and Done buttons move into the vertical bar too.

So the placement also decides how the toolbar looks. A sheet on the left keeps a horizontal toolbar at the top. A sheet on the right gets vertical controls. I covered that rule in Opt in to vertical bars on iPhone Duo.

Half-open

When iPhone Duo is partially folded, a sheet doesn't sit across the fold. That is the fold avoidance Apple describes for system components. So the sheet takes one half of the screen.

With .automatic, it goes to the left half.

.trailing puts it on the right half, with the controls in the vertical bar.

.center can't stay in the middle, because the middle is the fold. The sheet goes to the left half, the same as .automatic and .leading.

The placement is a preference, not a promise. The system still keeps the sheet off the fold.

Closed, and on other iPhones

On the outer display, the sheet fills the screen. The placement makes no difference. .leading and .trailing look the same. The controls go into the vertical bar, as they do for any sheet with a toolbar on the outer display.

It is the same on a regular iPhone. The sheet fills the width in both portrait and landscape, whatever the placement. You can add the modifier without checking which device you are on.

UIKit

In UIKit, set preferredPlacement on the sheet presentation controller before you present.

let newList = UINavigationController(rootViewController: NewListViewController())
if let sheet = newList.sheetPresentationController {
    sheet.preferredPlacement = .trailing
}
present(newList, animated: true)

The values are the same four: .automatic, .leading, .center, and .trailing.

According to the UIKit header, preferredPlacement is ignored when sourceView is set. A sheet with a source view centers itself over that view instead.

When to use it

The default is a good choice for most sheets. Reach for a placement when the side matters, for example:

• .trailing, when the sheet's actions should sit in the vertical bar, like the rest of your app's controls on the open device.
• .leading, when the sheet should keep a regular horizontal toolbar.
• .leading or .trailing, to keep one side of your layout visible next to the sheet.

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Summary

• presentationPlacement(_:) in SwiftUI and preferredPlacement in UIKit choose the side of a sheet. They are new in iOS 27.
• They make a difference on an open iPhone Duo, where the sheet doesn't fill the screen.
• .trailing puts the sheet next to the vertical bar, so its controls become vertical. .leading keeps them horizontal.
• When half-open, the sheet takes one half. .center can't sit over the fold and goes to the left half.
• Closed, and on a regular iPhone, the sheet fills the width, so the placement has no effect.