Note: PreviewUIKit

Using Xcode Previews for UIKit

**** Some project need to Disable Code Coverage for the scheme. (unchecking Code Coverage in Test section for scheme settings)

https://stackoverflow.com/questions/59705079/swiftui-canvas-preview-compile-error-undefined-symbols-for-architecture-x86-64

สามารถแก้ไขหน้าจอแสดงผลได้โดยแก้ previewLayout โดย Default จะเป็น รูปแบบ device .previewLayout(.fixed(width: 300.0, height: 40.0))

Preview UIView

#if canImport(SwiftUI) && DEBUG
import SwiftUI
import UIKit
@available(iOS 13.0, *)
struct ViewPreviews_Previews: PreviewProvider {
    static var previews: some View {
        UIViewPreview {
           // MARK: แปะ view ที่ต้องการจะ preview ตรงนี้
           return SomeUIView()
        }.previewLayout(.fixed(width: 300.0, height: 40.0))
    }
}
@available(iOS 13.0, *)
struct UIViewPreview<View: UIView>: UIViewRepresentable {
    let view: View
    init(_ builder: @escaping () -> View) {
        view = builder()
    }
    func makeUIView(context: Context) -> UIView {
        return view
    }
    func updateUIView(_ view: UIView, context: Context) {
        view.setContentHuggingPriority(.defaultHigh, for: .horizontal)
        view.setContentHuggingPriority(.defaultHigh, for: .vertical)
    }
}
#endif

Preview UIViewController

#if canImport(SwiftUI) && DEBUG
import UIKit
import SwiftUI

@available(iOS 13.0, *)
struct ViewControllerPreviews_Previews: PreviewProvider {
       static var previews: some View {
         UIViewControllerPreview {
           // MARK: แปะ view ที่ต้องการจะ preview ตรงนี้
           return SomeViewController()
         }
    }
}

@available(iOS 13.0, *)
struct UIViewControllerPreview<ViewController: UIViewController>: UIViewControllerRepresentable {
    func updateUIViewController(_ uiViewController: ViewController, context: Context) {}
    let viewController: ViewController

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

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

credit: https://www.swiftjectivec.com/using-xcode-previews-for-uikit/