SwiftUI: Achieving `sizeThatFits` Functionality on All iOS Versions for a SwiftUI Wrapper

Hello everyone,

I'm currently working on a SwiftUI wrapper for UIView and UIViewController, and my aim is to make this wrapper respect the size of the UIView and constraints.

For now, I have successfully implemented the sizeThatFits method from the UIViewRepresentable protocol, and it's working as expected. Here's my current implementation:

func sizeThatFits(_ width: CGFloat?, _ height: CGFloat?) -> CGSize? {
	let intrinsicContentSize = self.intrinsicContentSize
	let targetSize = CGSize(
		width: width ?? intrinsicContentSize.width,
		height: height ?? intrinsicContentSize.height
	guard targetSize.width != UIView.noIntrinsicMetric, targetSize.height != UIView.noIntrinsicMetric else {
		return nil
	let horizontalPriority: UILayoutPriority = width == nil ? .defaultLow : .defaultHigh
	let verticalPriority: UILayoutPriority = height == nil ? .defaultLow : .defaultHigh
	return systemLayoutSizeFitting(
		withHorizontalFittingPriority: horizontalPriority,
		verticalFittingPriority: verticalPriority

However, this method is only available from iOS 16 onwards. My goal is to provide the same functionality across all iOS versions.

I have experimented with various constraints and content compression/hugging priorities, but I have yet to achieve satisfying results.

Any suggestions or ideas on how to accomplish this would be greatly appreciated. Thank you!


SwiftUI is a private Apple framework - they have asked that those kinds of questions be asked on their developer forums. This forum is meant for discussion about the language itself and its open source development.

Or you could try Stack Overflow.

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