README.md

UIKit Previews

SwiftUI previews can be used for UIViewController and UIView in UIKit. Simply add the following structs to your UIKit application and then create the associated view providers.

UIViewController

ViewController.swift

import UIKit

final class ViewController: UIViewController {

    let button = UIButton()
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        button.translatesAutoresizingMaskIntoConstraints = false
        button.backgroundColor = .systemBlue
        button.setTitle("Button", for: .normal)
        view.addSubview(button)
        
        NSLayoutConstraint.activate([
            button.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            button.centerYAnchor.constraint(equalTo: view.centerYAnchor),
        ])
    }
}

#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

#if canImport(SwiftUI) && DEBUG
import SwiftUI

let deviceNames: [String] = [
    "iPhone SE",
    "iPhone 11 Pro Max",
    "iPad Pro (11-inch)"
]

@available(iOS 13.0, *)
struct ViewController_Preview: PreviewProvider {
  static var previews: some View {
    ForEach(deviceNames, id: \.self) { deviceName in
      UIViewControllerPreview {
        ViewController()
      }.previewDevice(PreviewDevice(rawValue: deviceName))
        .previewDisplayName(deviceName)
    }
  }
}
#endif

UIView

SimpleView.swift

import Foundation
import UIKit

final class SimpleView: UIView {
    
    let label = UILabel()
    
    override init(frame: CGRect) {
        super.init(frame: frame)
        
        label.translatesAutoresizingMaskIntoConstraints = false
        label.text = "Simple Label"
        
        addSubview(label)
        
        NSLayoutConstraint.activate([
            label.centerXAnchor.constraint(equalTo: centerXAnchor),
            label.centerYAnchor.constraint(equalTo: centerYAnchor)
        ])
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override var intrinsicContentSize: CGSize {
        return CGSize(width: 200, height: 200)
    }
}

#if canImport(SwiftUI) && DEBUG
import SwiftUI

@available(iOS 13, *)
public struct UIViewPreview<View: UIView>: UIViewRepresentable {
    public let view: View

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

    // MARK: - UIViewRepresentable
    public func makeUIView(context: Context) -> UIView {
        return view
    }

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

#if canImport(SwiftUI) && DEBUG
import SwiftUI

@available(iOS 13.0, *)
struct SimpleView_Preview: PreviewProvider {
  static var previews: some View {
    UIViewPreview {
      let button = SimpleView()
      return button
    }.previewLayout(.sizeThatFits)
     .padding(10)
  }
}
#endif

Links that help

• NSHipster Previews