resolve sizeThatFits not working on Xcode Preview using UIView

debug_preview.swift

import SwiftUI

// https://medium.com/@lyeskinnikitaalexandrovich/mastering-xcode-previews-with-snapkit-uikit-aa82a146059a
enum DebugPreviewLayout {
  case fitWidth(CGFloat)
  case fitHeight(CGFloat)
  case `default`
}

final class DebugPreviewLayoutView: UIView {
  private let childView: UIView
  private let previewLayout: DebugPreviewLayout
  private var childIntrinsicContentSize: CGSize? = nil
  
  override var intrinsicContentSize: CGSize {
    self.childIntrinsicContentSize ?? super.intrinsicContentSize
  }
  
  @available(*, unavailable)
  required init?(coder: NSCoder) {
    fatalError("init(coder:) has not been implemented")
  }
  
  init(previewLayout: DebugPreviewLayout, view: UIView) {
    self.childView = view
    self.previewLayout = previewLayout
    
    super.init(frame: .zero)
    
    self.configureUI()
    
    self.childIntrinsicContentSize = self.calculateChildSize()
  }
  
  override func invalidateIntrinsicContentSize() {
    self.childIntrinsicContentSize = self.calculateChildSize()
  }
  
  private func configureUI() {
    self.addSubview(self.childView)
    
    self.translatesAutoresizingMaskIntoConstraints = false
    self.childView.translatesAutoresizingMaskIntoConstraints = false
    
    self.childView.snp.makeConstraints {
      $0.edges.equalToSuperview()
    }
  }
  
  private func calculateChildSize() -> CGSize {
    var width = CGFloat.greatestFiniteMagnitude
    var height = CGFloat.greatestFiniteMagnitude
    var horizontalFittingPriority = UILayoutPriority.fittingSizeLevel
    var verticalFittingPriority = UILayoutPriority.fittingSizeLevel
    
    switch previewLayout {
    case let .fitHeight(value):
      height = value
      verticalFittingPriority = .required
    case let .fitWidth(value):
      width = value
      horizontalFittingPriority = .required
    default:
      break
    }

    return self.childView.systemLayoutSizeFitting(
      CGSize(width: width, height: height),
      withHorizontalFittingPriority: horizontalFittingPriority,
      verticalFittingPriority: verticalFittingPriority
    )
  }
}

struct DebugPreviewView<T: UIView>: UIViewRepresentable {
  private let previewLayout: DebugPreviewLayout
  private let viewBuilder: () -> T
  
  init(
    previewLayout: DebugPreviewLayout = .default,
    _ builder: @escaping () -> T
  ) {
    self.previewLayout = previewLayout
    self.viewBuilder = builder
  }
  
  // MARK: - UIViewRepresentable
  func makeUIView(context: Context) -> UIView {
    DebugPreviewLayoutView(
      previewLayout: self.previewLayout,
      view: self.viewBuilder()
    ).then {
      $0.invalidateIntrinsicContentSize()
    }
  }
  
  func updateUIView(_ view: UIView, context: Context) {
    view.setContentHuggingPriority(.defaultHigh, for: .vertical)
    view.setContentHuggingPriority(.defaultHigh, for: .horizontal)
  }
}