SwiftUI + UIKit.swift

import UIKit
import SwiftUI



class ViewController: UIViewController {

    var hosting: UIHostingController<SwiftUIView>?

    override func viewDidLoad() {
        super.viewDidLoad()
        let rootView = SwiftUIView(delegate: self, toggleStatus: false, stepper: 18)
        self.hosting = UIHostingController(rootView: rootView)

        self.addChild(hosting!)
        hosting!.view.frame = self.view.frame
        self.view.addSubview(hosting!.view)
    }

    func buttonPressed(toggleStatus: Bool) {
        let message = toggleStatus ? "on" : "off"
        
        let alert = UIAlertController(title: "hello", message: "The toggle is \(message)", preferredStyle: .alert)
        let ok = UIAlertAction(title: "OK", style: .default) { (_) in
            alert.dismiss(animated: true,
                          completion: nil)
        }
        alert.addAction(ok)
        self.present(alert, animated: true, completion: nil)
    }

}


struct SwiftUIView: View {
    weak var delegate: ViewController?
    
    @State var toggleStatus = false
    @State var stepper = 0
    
    func change() {
        self.toggleStatus = true
        self.stepper = 18
        print("change")
    }
    
    func checkup() -> Bool {
        return stepper <= 25 && toggleStatus == true
    }
    
    var body: some View {
        VStack {
            Text("Hello")
            
            Text("World")
            
            Spacer()
            
            Toggle(isOn: $toggleStatus, label: { Text("Toggle") })
            
            Stepper(value: $stepper, in: 0...999, label: { Text("\(stepper) years old") })
            
            Spacer()
            
            
            Button(action: {
                self.delegate?.buttonPressed(toggleStatus: self.toggleStatus)
            }) {
                Text("Press Me")
            }.disabled(checkup() == false)
        }
        .padding(.horizontal)
    }
}