Helpers to quickly create SwiftUI previews for the UIKit/AppKit view and view controller

_Example.swift

import SwiftUI

#if canImport(UIKit)
import UIKit

class ViewController: UIViewController {
    override func viewDidLoad() {
        super.viewDidLoad()
        view.backgroundColor = .systemYellow
        title = "Hello World!"
    }
}

@available(iOS 14.0, *) // This is only needed for .ignoresSafeArea()
struct ViewController_Previews: PreviewProvider {
    static var previews: some View {
        UIViewControllerRepresentableProvider { _ in
            let nav = UINavigationController(rootViewController: ViewController())
            nav.navigationBar.prefersLargeTitles = true
            return nav
        }
        .ignoresSafeArea()
        
        // For a UIView.
        UIViewRepresentableProvider { _ in
            let cell = UITableViewCell(style: .subtitle, reuseIdentifier: "")
            cell.textLabel?.text = "Hello"
            cell.detailTextLabel?.text = "World!"
            return cell
        }
    }
}

#endif

UIKitAppKitPreview.swift

///
/// Helpers to quickly create SwiftUI previews for the UIKit/AppKit view and view controller.
///
/// For example (UIKit):
/// ```
/// @available(iOS 14.0, *) // This is only needed for .ignoresSafeArea()
/// struct YourViewController_Previews: PreviewProvider {
///     static var previews: some View {
///         UIViewControllerRepresentableProvider { _ in
///             YourViewController()
///         }
///         .ignoresSafeArea()
///
///         // For a UIView.
///         UIViewRepresentableProvider { _ in
///             let cell = UITableViewCell(style: .subtitle, reuseIdentifier: "")
///             cell.textLabel?.text = "Hello"
///             cell.detailTextLabel?.text = "World!"
///             return cell
///         }
///     }
/// }
/// ```
///

import SwiftUI

#if canImport(UIKit) && DEBUG
import UIKit

struct UIViewControllerRepresentableProvider<T: UIViewController>: UIViewControllerRepresentable {
    
    /// Creates an instance of ``UIViewController`` for previewing.
    let makingUIViewController: (_ context: Context) -> T
    
    func makeUIViewController(context: Context) -> T {
        makingUIViewController(context)
    }
    
    func updateUIViewController(_ uiViewController: T, context: Context) {}
}

struct UIViewRepresentableProvider<T: UIView>: UIViewRepresentable {
    
    /// Creates an instance of ``UIView`` for previewing.
    let makingUIView: (_ context: Context) -> T
    
    func makeUIView(context: Context) -> T {
        makingUIView(context)
    }
    
    func updateUIView(_ uiView: T, context: Context) {}
}

#endif

#if canImport(AppKit) && DEBUG
import AppKit

struct NSViewControllerRepresentableProvider<T: NSViewController>: NSViewControllerRepresentable {
    
    /// Creates an instance of ``NSViewController`` for previewing.
    let makingNSViewController: (_ context: Context) -> T
    
    func makeNSViewController(context: Context) -> T {
        makingNSViewController(context)
    }
    
    func updateNSViewController(_ nsViewController: T, context: Context) {}
}

struct NSViewRepresentableProvider<T: NSView>: NSViewRepresentable {
    
    /// Creates an instance of ``NSView`` for previewing.
    let makingNSView: (_ context: Context) -> T
    
    func makeNSView(context: Context) -> T {
        makingNSView(context)
    }
    
    func updateNSView(_ nsView: T, context: Context) {}
}

#endif