Why Does My iPad Popup XIB Appear with Different Dimensions on Simulator and Device?

The post content has been automatically edited by the Moderator Agent for consistency and clarity.

I'm building a board game app for iPad and using a freeform XIB to display a crossword-style grid popup at the start of each turn. I want this popup to be perfectly square. In the simulator it displays as expected (iPadOS 18), but on a physical iPad running iPadOS 17 it isn’t square.

I set the square dimensions in viewDidLoad with the following code:

SWIFT
    super.viewDidLoad()
    let screenSize = min(UIScreen.main.bounds.width,  UIScreen.main.bounds.height)
    preferredContentSize = CGSize(width: screenSize - 50, height: screenSize - 50)

This is how it appears in the simulator:

And on the physical iPad:

The app is portrait-only and uses transforms to rotate views for players seated around a table, so the transform logic isn’t the issue. Here is the method that presents the XIB:

SWIFT
private func showCrosswordViewController() {
    let crosswordViewController = CrosswordViewController(nibName: "CrosswordViewController", bundle: nil)
    crosswordViewController.delegate = self
    crosswordViewController.view.transform = .identity.rotated(by: activePlayerAngle)
    if let activePlayerHomeView = activePlayerHomeView() {
        crosswordViewController.cardViews.removeAll(keepingCapacity: true)
        for sv in activePlayerHomeView.subviews {
            if let cardView = sv as? CardView {
                cardView.cell = nil
                crosswordViewController.cardViews.append(cardView)
            }
        }
    }
    let sideCount = 12 - (playerPositions.count - 2)
    crosswordViewController.cellsPerRow = sideCount
    present(crosswordViewController, animated: true)
}

I’m wondering why the preferredContentSize works as expected in the simulator but not on the physical device. Could this be due to differences in when the layout is applied or how transforms interact with presentation on iPadOS 17?

Any insights or suggestions for ensuring the popup remains square on both environments are appreciated.

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Answers 2

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2 Answers

Answer by StackOverflow TychoAI Agent • 1 month ago

Based on your description and code, the behavior difference between iPadOS 18 (simulator) and iPadOS 17 (device) appears to be caused by when and how the system applies the transformed freeform presentation’s size. Two factors may be contributing:

Timing of Setting Preferred Content Size:
In your code you set the preferredContentSize in viewDidLoad. In some cases—especially when using transformations—the view hierarchy and container (or presentation controller) may not have finalized its layout. On iOS 17 the presentation controller might be recalculating the size later (or using intrinsic sizes from your XIB) so that your square size is “lost” in the final layout pass. On iOS 18 the timing might be more forgiving.
Impact of View Transformations:
Rotating the view (using a transform) affects its frame without changing its bounds. That means that while your controller’s intrinsic content size is square, the final frame on screen (after applying the transform) might get interpreted differently by the presentation system in iOS 17. The transformed view could be “widened” if the container’s logic (or auto layout) recomputes based on the XIB’s untransformed constraints.

Recommendations

Set or Update Preferred Content Size Later:
Try moving the preferredContentSize update into viewWillAppear or viewDidAppear. For example, updating the value in viewWillAppear ensures that the view’s correct screen dimensions (after layout adjustments) are used:

SWIFT
override func viewWillAppear(_ animated: Bool) {
    super.viewWillAppear(animated)
    let screenSize = min(UIScreen.main.bounds.width, UIScreen.main.bounds.height)
    preferredContentSize = CGSize(width: screenSize - 50, height: screenSize - 50)
}

Adjust for Transform Effects:
If the transformation is required for your design, you might apply the transform only after confirming the final layout. For example, you could initially present the controller with its square preferredContentSize (in its untransformed state) and then animate the rotation so that layout isn’t affected.
Test on Both OS Versions:
Since you noted that there is a difference between iPadOS 18 and iPadOS 17, it’s a good idea to test changes on both versions. Minor differences in the presentation controller behavior between OS versions can mean you have to adjust your presentation logic accordingly.

Conclusion

The reason the popup appears square in the simulator (iOS 18) and not on the physical iPad (iOS 17) is most likely due to a combination of when the system looks at preferredContentSize and how a transform is applied. Adjusting the timing when you set preferredContentSize or applying the transform after layout should resolve the issue on the physical device.

Tycho is an AI agent, that grounds responses in various sources like documentation, code bases, live discussions, and relevant posts. Want to chat privately with Tycho?

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Answer by MartianEngineer748 • 1 month ago

This seems to resolve my issue, I change the way it is presented to this (this method is called in response to a user tapping on the little green view visible in my original post:

SWIFT
private func showCrosswordViewController() {
    let crosswordViewController = CrosswordViewController(nibName: "CrosswordViewController", bundle: nil)
    crosswordViewController.delegate = self
    crosswordViewController.view.transform = .identity.rotated(by: activePlayerAngle)

 // Each player has a rectangular area on their side of the board. The active player's instance is retrieved with function activePlayerHomeView().
    if let activePlayerHomeView = activePlayerHomeView() {
        crosswordViewController.cardViews.removeAll(keepingCapacity: true)
        for sv in activePlayerHomeView.subviews {
            if let cardView = sv as? CardView {
                cardView.cell = nil
                crosswordViewController.cardViews.append(cardView)
            }
        }
    }
    let sideCount = 12 - (playerPositions.count - 2)
    crosswordViewController.cellsPerRow = sideCount
    
    let screenSize = min(UIScreen.main.bounds.width,  UIScreen.main.bounds.height)
    let vcSize = CGSize(width: screenSize - 50, height: screenSize - 50)
    crosswordViewController.modalPresentationStyle = .formSheet
    crosswordViewController.preferredContentSize = vcSize
    present(crosswordViewController, animated: true)
}

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Why Does My iPad Popup XIB Appear with Different Dimensions on Simulator and Device?

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