SwiftUI iPhone Duo

Do not design a separate “Duo version” of the app.

Start with an adaptive SwiftUI interface that works across continuously changing widths and heights. Add Duo-specific behavior only when the fold, hinge, second display, or vertical system bars materially improve the experience.

The target is not “Make this app support iPhone Duo.” The target is:

Make this app excellent at every size, then use Duo's unique hardware where it creates additional value.

Before reviewing or changing layout, read the full rulebook: reference.md.

When to use

• User asks to support iPhone Duo, a foldable iPhone, hinge, fold, or two displays.
• User asks for adaptive SwiftUI layout across compact → wide, including multitasking.
• Code uses UIDevice, UIScreen.main (bounds or scale), idiom, orientation, isDuo, or isFolded for layout.
• Work involves vertical bars, toolbar item ordering/overflow, sheet placement, ArrangementView, reserved regions, onHingeChange / UIHingeInteraction, or CameraCaptureAccessory.
• The project moves to the iOS 27.1 SDK (that build is what turns on full-screen layout and vertical bars).