Compatibility with existing AppDelegate based app.

UI Frameworks UIKit
arnaud-sch OP
Created 12h
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This post is from the Activity iPhone Duo UIKit Q&A.

I have an app mixing UIKit and SwiftUI. Right now it’s not yet migrated to SceneDelegate. What will happen when the iPhone Duo is available ? Will the app run, or crash ?

Answered by DTS Engineer in 906442022

While your app is compiled with an SDK version prior to iOS 27, such as with Xcode 26, it will run in a compatibility mode on iPhone Duo — you can see an example of what that looks like in Prepare your app for iPhone Duo. Once you rebuild with Xcode 27, the scene lifecycle becomes required, and this is not unique to iPhone Duo. Transitioning to the UIKit scene-based life cycle has the information you need to succeed with the migration to the scene-based lifecycle.

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DTS Engineer OP
Apple
11h
Accepted Answer

While your app is compiled with an SDK version prior to iOS 27, such as with Xcode 26, it will run in a compatibility mode on iPhone Duo — you can see an example of what that looks like in Prepare your app for iPhone Duo. Once you rebuild with Xcode 27, the scene lifecycle becomes required, and this is not unique to iPhone Duo. Transitioning to the UIKit scene-based life cycle has the information you need to succeed with the migration to the scene-based lifecycle.
hotpaw2 OP
11h

My experience is that when an app without a scene delegate is built with Xcode 26, it will run on an iOS 27 device. If built with Xcode 27, it will crash on launch.

Compatibility with existing AppDelegate based app.
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