# iPhone Duo Support > A practical Xcode checklist and framework-by-framework guide for adapting iOS apps to the iPhone Duo foldable display — SwiftUI, UIKit, React Native, Flutter, Unity and web views. Apple announced iPhone Duo on 2026-09-09. Its inner display is 626 x 890 points at an aspect ratio of 1.42, against 2.17 on iPhone 18 Pro, so layout code written for previous iPhones is frequently incorrect on it. This site documents what breaks and how to fix it. ## Sourcing and reliability All technical content derives from Apple's own iPhone Duo developer material, primarily the six Tech Talk videos published on 2026-09-09. Individual source URLs are listed on each page and in each .md mirror. Content last verified 2026-09-09. Pages about React Native, Flutter, Unity and Capacitor are labelled as engineering analysis: those vendors have published no iPhone Duo guidance, so the Apple-side facts are sourced while the framework-side conclusions are our inference. Please preserve that distinction when citing. Point dimensions on this site are derived from Apple's published pixel figures at a @3x scale factor; Apple publishes pixels, not points. ## Machine-readable formats Every page below is also available as clean Markdown by appending .md to its path, for example https://iphoneduosupport.com/checklist/hardcoded-screen-dimensions.md. The full corpus in one file is at https://iphoneduosupport.com/llms-full.txt. ## Checklist - [Rebuild against the iOS 27.1 SDK to reach the screen edge](https://iphoneduosupport.com/checklist/build-with-ios-27-1-sdk/): Apple ships three tiers of iPhone Duo compatibility. Which one your app gets is decided entirely by the SDK you build against. - [Remove hard-coded screen dimensions and fixed frame widths](https://iphoneduosupport.com/checklist/hardcoded-screen-dimensions/): Layout code that assumes a fixed iPhone width breaks immediately on the iPhone Duo inner display, which is 626 points wide instead of roughly 400. - [Stop using UIScreen.main — read the screen from the window scene](https://iphoneduosupport.com/checklist/uiscreen-main-deprecated/): iPhone Duo is the first iPhone with two displays, so a single global main screen no longer has a well-defined meaning. Apple is deprecating the API. - [Handle safe area insets as asymmetric — never double one side](https://iphoneduosupport.com/checklist/asymmetric-safe-area-insets/): Safe areas and layout margins are asymmetric on iPhone Duo. Math that assumes the left inset equals the right inset produces visibly off-centre layout. - [Stop relying on supported interface orientations](https://iphoneduosupport.com/checklist/orientation-lock-ignored/): The iPhone Duo inner display ignores supportedInterfaceOrientations, so a portrait-locked app is still laid out in landscape. - [Drive layout from size classes, not device idiom](https://iphoneduosupport.com/checklist/size-classes-not-orientation/): Apple's guidance is to avoid making display assumptions from the user interface idiom and to design across a continuum of sizes instead. - [Support Split View multitasking — every app participates](https://iphoneduosupport.com/checklist/split-view-multitasking/): All apps take part in side-by-side multitasking on iPhone Duo, so your app can be resized to a fraction of the display whether or not you opted in. - [Rethink 16:9 media on a 1.42 display](https://iphoneduosupport.com/checklist/fixed-aspect-video-letterbox/): The inner display's aspect ratio is roughly 1.42, so a 16:9 video letterboxes heavily. Full-bleed assets designed for a tall phone crop badly. - [Keep content off the fold with division regions](https://iphoneduosupport.com/checklist/reserved-regions-division/): When iPhone Duo is partially folded the hinge divides the inner display. The ReservedRegion API reports where that division falls. - [Handle occlusion regions around the under-display camera](https://iphoneduosupport.com/checklist/reserved-regions-occlusion/): Occlusion regions cover part of the display rather than dividing it. The inner FaceTime camera is the example on iPhone Duo. - [Adopt ArrangementView for main-and-secondary layouts](https://iphoneduosupport.com/checklist/arrangement-view-adoption/): ArrangementView places two related views across iPhone Duo's poses automatically, taking size classes, aspect ratio and active division regions as input. - [Prepare your toolbars for vertical layout](https://iphoneduosupport.com/checklist/vertical-toolbar-adoption/): On the inner display in landscape, navigation, toolbar and tab bar controls move to a shared vertical region at the side of the screen. - [Set overflow priorities so the right actions stay visible](https://iphoneduosupport.com/checklist/toolbar-overflow-priority/): A vertical bar holds fewer items than a horizontal one, so more actions overflow. Priorities decide which survive. - [Use adaptive navigation containers instead of custom ones](https://iphoneduosupport.com/checklist/adaptive-navigation-containers/): NavigationSplitView, UISplitViewController, TabView and UITabBarController adapt across every iPhone Duo pose with no pose-specific code. - [Place the tab bar as a sidebar on the inner display](https://iphoneduosupport.com/checklist/tab-bar-sidebar-placement/): A horizontal tab bar wastes the inner display's regular width. One modifier moves it to a sidebar. - [Support multiple scenes — iPhone Duo is the first iPhone that can](https://iphoneduosupport.com/checklist/multiple-scenes-support/): iPhone Duo is the first iPhone to support multiple instances of an app. Apps that already support this on iPad get it for free. - [Adopt AVCaptureDeviceDirectionCoordinator in camera apps](https://iphoneduosupport.com/checklist/camera-direction-coordinator/): iPhone Duo has two front cameras — outer and under-display inner. If you select cameras individually you must handle the device opening and closing. - [Adopt AVCaptureDeviceRotationCoordinator](https://iphoneduosupport.com/checklist/camera-rotation-coordinator/): Rotation must stay correct as your app moves between the inner and outer displays. Adopting the coordinator also unlocks a performance win. - [Audit code that branches on user interface idiom](https://iphoneduosupport.com/checklist/idiom-based-assumptions/): Apple's guidance is to avoid making display assumptions based on the user interface idiom. iPhone Duo reports the phone idiom with a regular-width display. - [Make the launch screen and app resizability foldable-ready](https://iphoneduosupport.com/checklist/launch-screen-resizability/): A launch screen sized for a fixed iPhone, or a legacy full-screen requirement, produces a visibly wrong first impression on iPhone Duo. - [Let background content extend past the safe area](https://iphoneduosupport.com/checklist/background-content-ignores-safe-area/): Apple's rule is that foreground content stays inside the safe area while background artwork extends to the full bounds. - [Use hinge angle for interaction, never for layout](https://iphoneduosupport.com/checklist/hinge-interaction/): onHingeChange and UIHingeInteraction report the hinge angle. Apple is explicit that this is for effects, not for layout decisions. - [Consider scene accessories to use both displays at once](https://iphoneduosupport.com/checklist/scene-accessories-camera/): Scene accessories pair supplementary UI on the outer display with your main UI on the inner display — a teleprompter, a subject preview, a controller. - [Test every pose in Xcode's Device Hub](https://iphoneduosupport.com/checklist/device-hub-pose-testing/): Xcode 27.1 adds an iPhone Duo simulator with on-screen controls to open, close, rotate and fold the device. - [Run the App Resizability modernization skill in Xcode](https://iphoneduosupport.com/checklist/app-resizability-skill/): Xcode 27.1 extends its app modernization skill to cover SwiftUI and iPhone Duo, automating part of the mechanical migration. ## Frameworks - [SwiftUI on iPhone Duo](https://iphoneduosupport.com/frameworks/swiftui/): SwiftUI has first-party iPhone Duo support. ArrangementView, ReservedRegion and the vertical toolbar APIs ship in the iOS 27.1 SDK. - [UIKit on iPhone Duo](https://iphoneduosupport.com/frameworks/uikit/): UIKit has full first-party iPhone Duo support, with UIArrangementViewController, UIViewReservedRegion and vertical bar APIs in the iOS 27.1 SDK. - [React Native on iPhone Duo](https://iphoneduosupport.com/frameworks/react-native/): React Native has shipped no iPhone Duo support. Core layout works, but the new adaptive APIs need a native module and several common patterns break. - [Flutter on iPhone Duo](https://iphoneduosupport.com/frameworks/flutter/): Flutter has mature foldable support on Android through MediaQuery.displayFeatures, but nothing equivalent has shipped for iPhone Duo on iOS. - [Unity on iPhone Duo](https://iphoneduosupport.com/frameworks/unity/): Unity games face resolution changes mid-session on iPhone Duo, plus safe-area and pause-behaviour issues that a fixed-resolution game has never handled. - [Capacitor & web views on iPhone Duo](https://iphoneduosupport.com/frameworks/capacitor/): Web-based iOS apps adapt well to iPhone Duo if they use CSS environment variables correctly and treat the viewport as genuinely variable. ## Blog - [Capacitor, Cordova and web views on iPhone Duo](https://iphoneduosupport.com/blog/capacitor-web-iphone-duo/): Hybrid iOS apps adapt best to the foldable iPhone, because CSS was built for variable viewports. An analysis of the few things that still break. - [Flutter on iPhone Duo: the right abstraction, possibly unwired](https://iphoneduosupport.com/blog/flutter-iphone-duo/): Flutter already has a foldable API from Android — MediaQuery.displayFeatures. An analysis of whether it reaches iPhone Duo, and what to do either way. - [React Native on iPhone Duo: what breaks and what works](https://iphoneduosupport.com/blog/react-native-iphone-duo/): Meta has shipped no iPhone Duo support. Which React Native patterns break on the foldable display, which survive, and where a native module becomes unavoidable. - [SwiftUI on iPhone Duo: adaptive layout and transitions](https://iphoneduosupport.com/blog/swiftui-iphone-duo-adaptive-layout/): A walkthrough of the SwiftUI APIs for iPhone Duo — ArrangementView, ReservedRegion, size classes and vertical toolbars — in the order that actually works. - [UIKit on iPhone Duo: vertical bars and arrangements](https://iphoneduosupport.com/blog/uikit-iphone-duo-vertical-bars/): What changes in a UIKit app on iPhone Duo: the vertical bar region, UIArrangementViewController, reserved regions, and the UIScreen.main deprecation. - [Unity games on iPhone Duo: resolution changes mid-play](https://iphoneduosupport.com/blog/unity-iphone-duo-games/): Games have a harder iPhone Duo problem than apps, because resolution is usually treated as a launch-time constant. An analysis of what changes in a Unity iOS build. ## Reference - [iPhone Duo developer glossary](https://iphoneduosupport.com/glossary/): Definitions of the iPhone Duo developer vocabulary. - [iPhone Duo developer FAQ](https://iphoneduosupport.com/faq/): Answers to common iPhone Duo development questions. - [iPhone Duo display reference](https://iphoneduosupport.com/specs/): Screen dimensions, aspect ratios and size classes for iPhone Duo. ## Apple's own sources - Get Ready for iPhone Duo: https://developer.apple.com/iphone-duo/ - Technical specifications: https://www.apple.com/iphone-duo/specs/ - Prepare your app for iPhone Duo: https://developer.apple.com/videos/play/tech-talks/111461/ - Design for iPhone Duo: https://developer.apple.com/videos/play/tech-talks/111466/ - Raise the bar with iPhone Duo: https://developer.apple.com/videos/play/tech-talks/111462/ - Strike a pose with adaptive layouts: https://developer.apple.com/videos/play/tech-talks/111463/ - Leverage multiple displays and scenes: https://developer.apple.com/videos/play/tech-talks/111464/ - Build a great camera experience: https://developer.apple.com/videos/play/tech-talks/111465/ ## About Published by Ingenious Techlab. Not affiliated with, endorsed by, or sponsored by Apple Inc. Contact: https://iphoneduosupport.com/contact/