Generic structures to host previews of UIView and UIViewController subclasses.

UIViewControllerPreview.swift

import UIKit

#if canImport(SwiftUI) && DEBUG
import SwiftUI
struct UIViewControllerPreview<ViewController: UIViewController>: UIViewControllerRepresentable {
    let viewController: ViewController

    init(_ builder: @escaping () -> ViewController) {
        viewController = builder()
    }

    // MARK: - UIViewControllerRepresentable

    func makeUIViewController(context: Context) -> ViewController {
        viewController
    }

    func updateUIViewController(_ uiViewController: ViewController, context: UIViewControllerRepresentableContext<UIViewControllerPreview<ViewController>>) {
        return
    }
}
#endif

UIViewPreview.swift

import UIKit

#if canImport(SwiftUI) && DEBUG
import SwiftUI
struct UIViewPreview<View: UIView>: UIViewRepresentable {
    let view: View

    init(_ builder: @escaping () -> View) {
        view = builder()
    }

    // MARK: - UIViewRepresentable

    func makeUIView(context: Context) -> UIView {
        return view
    }

    func updateUIView(_ view: UIView, context: Context) {
        view.setContentHuggingPriority(.defaultHigh, for: .horizontal)
        view.setContentHuggingPriority(.defaultHigh, for: .vertical)
    }
}
#endif