iPhone Duo UIKit Q&A

I’m using a UITabBarController with fixed UITabs and sidebarOnly UITabs, on an iPhone Duo I’m seeing the sidebarOnly tabs show up regardless of sidebar.preferredPlacement. Is this expected? I’m trying to achieve the same behavior as the Health app as shown in the developer videos. I have a feeling that I might need to check for the horizontal size class, but I feel like the API should be doing the work of hiding the sidebarOnly tabs, no? Also, when setting tabBarController.sidebar.preferredPlacement = .sidebar and collapse it I don’t see the sidebar when I collapse on the inner display using Xcode 27.1. I think this is a bug?

We ship a large production app that mixes UIKit and SwiftUI. We're planning our iPhone Duo support, but until we adopt the latest SDK, we want to understand how compatibility mode applies to our current builds. Is there a canonical way to preview our app in compatibility mode across all iPhone Duo poses? We can build with Xcode 26.6 and run on the iPhone Duo simulator, but we can't switch poses and it's unclear whether that matches the real compatibility mode on device. We'd like to see how the app responds to each pose so we're confident in the experience users will get at launch.

It would be great if Apple could provide a sample app covering all the cases for iPhone Duo, an app that follows best practices when it comes to handling UI and works on normal iPhones, iPhone Duo and iPad. Also if I remember correctly it's been a long time since we got a UIKit sample app.

When the inner camera is in use and the reserved region becomes active, what is the recommended way for apps to adapt their UI? Should content move out of the reserved region where possible, or is it generally acceptable to leave content behind it? More specifically, how should apps handle content that can’t easily move aside, such as a long navigation title directly behind the reserved region? Should it be truncated, moved below the region, or handled another way?

We have built our existing app with Xcode 27.1 and when running it on iPad it does not resize - it seems to run in iPhone mode as usual, in a fixed portrait mode. However the same build will resize to a wider aspect ratio in iPhone mirroring (and on Duo, obviously) But, the app when built with Xcode 27 does resize on an iPad. So is the 27.1 iPad behaviour expected or is this just something temporary in the 27.1 beta?

When the user transitions from an open to a partially folded state, the system detects this is the final state after some delay and un-blurs the left side. The UI should now adapt to this state. For example, split view controller enlarges the sidebar to occupy the full width of the left side. What’s the best trigger to use for a custom view controller that wants to achieve a similar result? Is it the folding region becoming active?

My app has a small inputAccessoryView that does not fill the width of the screen above the keyboard. On iPhone Duo with a vertical toolbar, tapping in my text view to bring up the keyboard will collapse all bar buttons that are obscured by the keyboard and any that intersect the vertical space of my inputAccessoryView, even though the inputAccessoryView does not visually overlap the vertical bar. Is there a way to keep more bar buttons on screen?

In the iPhone Duo horizontal pose full expanded inner screen, we use UITabBarController (set up using the viewControllers property), and the UITabBar is still horizontal when it should be vertical ? What are the best practices to make it always adaptable in all poses ?

When the inner screen on iPhone Duo is partially folded and horizontal, what is the best practice to make the UITabAccessory adapt ? How to make it shift to the left or to the right screen and how to size it properly in that case ?

We're supposed to keep away from the centre of the screen when Duo is half-folded (some sort of book / laptop-like pose). How do I do it in a right/intended by UIKit engineers way? Sub-Questions below: a) What's the proper way in UIKit, if I only have a frame of region? b) How to understand if division region is vertical or horizontal, and where shall i move my controls out of center? c) Do we get any layout guides for that?

Can an iPhone-only app that fully supports iPhone Duo, but is not otherwise optimized for iPad (and is non-universal), opt out of free-form resizing on iPad?

Cold launch from a shortcut, universal link, or push is handled in scene(_:willConnectTo:options:). Diiferent functionalities also start Live Activities and reload widgets. If the device is folded, does that scene connect for the outer display, and can the geometry still change before the first frame if the user unfolds? When folded, do Live Activities and widgets appear on the outer display, and is there a separate presentation the app must support?

Only Home updates layout when the size class changes. Various screens are pushed and set their table and scroll heights once from the screen size. Does every controller in a navigation stack, including ones that are not visible, receive viewWillTransition(to:with:)? For forms and lists on the inner display, is readableContentGuide the width we should use, and does it update during the fold?

On the unfolded inner display our root view controller’s horizontalSizeClass becomes .regular, the same as iPad. Folded, it is .compact. Is that the supported way to tell the two displays apart, or is there a Duo-specific trait, screen idiom, or UIWindowScene property we should use instead of size class?

We resume location and refresh Home from sceneDidBecomeActive, and we ignore that callback while Apple Pay is up because dismissing PKPaymentAuthorizationController also makes the scene active. Does a fold or unfold call sceneWillResignActive, sceneDidEnterBackground, or sceneDidBecomeActive? If the user folds during Apple Pay, does the payment sheet dismiss and complete, or stay up on the other display?

The QR scanner uses AVCaptureSession and an AVCaptureVideoPreviewLayer framed to the view bounds. Different screens present UIImagePickerController with source type .camera. If the user folds or unfolds while either is visible, which camera stays active, does the preview orientation and frame update, and is the picker dismissed or left at the old display size?

In our app we have situations where the user may be blocked for security reasons and we currently present a full screen modal - can we fill the screen with a modal in such a situation on Duo if the app is full screen on the inner display?

Camera, gallery, and PDF choices use UIAlertController style .actionSheet with no popover source. Receipt sharing uses UIActivityViewController, and uploads use UIDocumentPickerViewController; only some set sourceView, and almost none set a real sourceRect. On iPad those presentations need an anchor. On the unfolded Duo display, where the size class is regular, does UIKit still present them as phone sheets, or must every one set sourceView and sourceRect?

Given the size-class behavior mirrors iPad in the unfolded state, does UIDevice.current.userInterfaceIdiom (and UITraitCollection.userInterfaceIdiom) still report .phone in both postures, or does it change to .pad-like when unfolded? This affects any idiom-based branching in our codebase.

Which parameters are exactly used to decide which controls are moving to the vertical bar? What are they (which priorities, other properties are used for that decision?)