VisionOS app with UIKit: app crashed when window created programatically

Question

I have a basic UIKit app (created from Xcode template), and modified it to remove loading from storyboard, because I want to create the app’s window programmatically instead of using a storyboard. This works fine when the app is run in an iPhone or iPad simulator, but the app crashes when run on an Apple Vision simulator (when building with the visionOS SDK).

This is the code I use to create the window in the SceneDelegate class:

func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
        print("SceneDelegate - willConnectTo session")
        guard let windowScene = scene as? UIWindowScene else { return }
        window = UIWindow(windowScene: windowScene)
        window?.backgroundColor = UIColor.systemBackground
        window?.rootViewController = ViewController()
        window?.makeKeyAndVisible() // crashes here in Apple Vision device
    }

The crash I get is at the “window?.makeKeyAndVisible” line: *** Assertion failure in BOOL _UIWindowSceneCompatibleIsHidden(UIWindow *__strong)(), UIWindowScene.m:2732

Here is the stack trace that the Xcode debugger shows:

*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Error in UIKit client: window visibility must match its layer visibility!'
*** First throw call stack:
(
    0   CoreFoundation                      0x00000001804a510c __exceptionPreprocess + 172
    1   libobjc.A.dylib                     0x0000000180082f50 objc_exception_throw + 56
    2   Foundation                          0x0000000180d41024 -[NSMutableDictionary(NSMutableDictionary) classForCoder] + 0
    3   UIKitCore                           0x0000000185570000 _UIWindowSceneCompatibleIsHidden + 200
    4   UIKitCore                           0x0000000185570ca4 -[UIWindowScene _windowUpdatedVisibility:] + 212
    5   UIKitCore                           0x000000018532f264 -[UIWindow _updateLayerOrderingAndSetLayerHidden:actionBlock:] + 188
    6   UIKitCore                           0x0000000185330128 -[UIWindow _setHidden:forced:] + 228
    7   UIKitCore                           0x000000018533f024 -[UIWindow _mainQueue_makeKeyAndVisible] + 36
    8   TestMultiWindowCDApp                0x00000001047d073c $s20TestMultiWindowCDApp13SceneDelegateC5scene_13willConnectTo7optionsySo7UISceneC_So0L7SessionCSo0L17ConnectionOptionsCtF + 844
    9   TestMultiWindowCDApp                0x00000001047d08a8 $s20TestMultiWindowCDApp13SceneDelegateC5scene_13willConnectTo7optionsySo7UISceneC_So0L7SessionCSo0L17ConnectionOptionsCtFTo + 84
    10  UIKitCore                           0x00000001847ef76c +[UIScene _sceneForFBSScene:create:withSession:connectionOptions:] + 1012
    11  UIKitCore                           0x00000001852fafd0 -[UIApplication _connectUISceneFromFBSScene:transitionContext:] + 804
    12  UIKitCore                           0x00000001852fb2b8 -[UIApplication workspace:didCreateScene:withTransitionContext:completion:] + 356
    13  UIKitCore                           0x0000000184dda1b4 -[UIApplicationSceneClientAgent scene:didInitializeWithEvent:completion:] + 260
    14  FrontBoardServices                  0x0000000186e4851c -[FBSScene _callOutQueue_didCreateWithTransitionContext:completion:] + 296
    15  FrontBoardServices                  0x0000000186e71d48 __92-[FBSWorkspaceScenesClient createSceneWithIdentity:parameters:transitionContext:completion:]_block_invoke.90 + 224
    16  FrontBoardServices                  0x0000000186e55390 -[FBSWorkspace _calloutQueue_executeCalloutFromSource:withBlock:] + 160
    17  FrontBoardServices                  0x0000000186e71ac0 __92-[FBSWorkspaceScenesClient createSceneWithIdentity:parameters:transitionContext:completion:]_block_invoke + 284
    18  libdispatch.dylib                   0x0000000105a567e4 _dispatch_client_callout + 16
    19  libdispatch.dylib                   0x0000000105a5a3dc _dispatch_block_invoke_direct + 392
    20  FrontBoardServices                  0x0000000186e95aa8 __FBSSERIALQUEUE_IS_CALLING_OUT_TO_A_BLOCK__ + 44
    21  FrontBoardServices                  0x0000000186e95984 -[FBSMainRunLoopSerialQueue _targetQueue_performNextIfPossible] + 196
    22  FrontBoardServices                  0x0000000186e95adc -[FBSMainRunLoopSerialQueue _performNextFromRunLoopSource] + 24
    23  CoreFoundation                      0x0000000180405be8 __CFRUNLOOP_IS_CALLING_OUT_TO_A_SOURCE0_PERFORM_FUNCTION__ + 24
    24  CoreFoundation                      0x0000000180405b30 __CFRunLoopDoSource0 + 172
    25  CoreFoundation                      0x00000001804052f8 __CFRunLoopDoSources0 + 320
    26  CoreFoundation                      0x00000001803ff9b8 __CFRunLoopRun + 768
    27  CoreFoundation                      0x00000001803ff2b4 CFRunLoopRunSpecific + 572
    28  GraphicsServices                    0x000000018e9b6c20 GSEventRunModal + 160
    29  UIKitCore                           0x00000001852f9c70 -[UIApplication _run] + 868
    30  UIKitCore                           0x00000001852fd910 UIApplicationMain + 124
    31  UIKitCore                           0x000000018478b890 __swift_destroy_boxed_opaque_existential_1Tm + 10528
    32  TestMultiWindowCDApp                0x00000001047cf67c $sSo21UIApplicationDelegateP5UIKitE4mainyyFZ + 120
    33  TestMultiWindowCDApp                0x00000001047cf5f4 $s20TestMultiWindowCDApp11AppDelegateC5$mainyyFZ + 44
    34  TestMultiWindowCDApp                0x00000001047cf750 main + 28
    35  dyld                                0x0000000104e9d544 start_sim + 20
    36  ???                                 0x000000010482e058 0x0 + 4370653272
    37  ???                                 0x2311800000000000 0x0 + 2526941603419914240
)
libc++abi: terminating due to uncaught exception of type NSException

I do get a window object when I use UIWindow(windowScene: windowScene)

Any ideas what this error means, and/or how to resolve it?

Answer 1

For some reason, it works if I comment out the line window?.backgroundColor = UIColor.systemBackground