Mac Catalyst Modally Presented View Controllers Not Working in Xcode Live Previews

Question

Created Sep ’23

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I have a UIViewController subclass I'm using in Mac Catalyst. This view controller is only ever presented as a sheet. When I try to make a live preview for it the preview is displayed a gigantic size (not the sheet's actual size at runtime). I made a separate thread about this: https://developer.apple.com/forums/thread/738641

In order to be able to preview the view controller for Mac Catalyst at the desired size I figured I'd present it on another view controller.

#Preview {
    let wrapperVC = WrapperViewController()
    return wrapperVC
}

//In WrapperViewController
   override func viewDidAppear(_ animated: Bool)
    {
        super.viewDidAppear(animated)
        if (firstViewDidAppear)
        {
            firstViewDidAppear = false
            view.backgroundColor = UIColor.yellow
            let realVC = ActualVCIWantToPreview()
            realVC.modalPresentationStyle = .formSheet
            present(realVC, animated: false);
        }
    }

But that's not working. However if I change the device from Mac to iPad it does work so it appears modal presentations aren't working for Live Previews on Mac Catalyst (unless I'm doing something wrong but Xcode is reporting no errors it just isn't showing my presented view controller).

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Answer 1

Macho Man Randy Savage OP

Sep ’23

If I hit the "Play" button in the Preview my app icon appears in the dock and it says "Previewing on 'Local Mac'" and there is a button that says "Bring Forward" but I see nothing.

If I click the "Bring Forward" button it launches the preview (my app?) and it shows me the view controller I'm previewing and it does perform the modal presentation in the window brought forward.

.....but if I make a change to the source code this window doesn't refresh it stops the preview and I have to relaunch it. I don't see how this is any different from launching my app normally as the preview is not live.

Are Mac "Live Previews" supposed to behave this way or is this a bug?

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