gistfile1.txt

//: A UIKit based Playground for showing KVO in Swift.
  
import UIKit
import PlaygroundSupport

final class MyViewController : UIViewController {
    @objc var model: MyModel = MyModel()
    var intValueObserver: NSKeyValueObservation!
    
    weak var label: UILabel!
    weak var button: UIButton!
    
    @objc func incrementTouchUpInside(_ sender: UIButton) {
        model.increment()
    }
    
    func updateLabel() {
        self.label.text = "\(model.intValue)"
    }
    
    // MARK: UIViewController
    
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white

        let label = UILabel()
        view.addSubview(label)
        self.label = label
        label.translatesAutoresizingMaskIntoConstraints = false
        view.topAnchor.constraint(equalTo: label.topAnchor, constant: -150).isActive = true
        view.centerXAnchor.constraint(equalTo: label.centerXAnchor, constant: 0).isActive = true
        label.textColor = .black
        
        let button = UIButton()
        button.setTitleColor(UIColor.systemBlue, for: .normal)
        button.setTitle("Increment", for: .normal)
        button.addTarget(self, action: #selector(incrementTouchUpInside(_:)), for: .touchUpInside)
        view.addSubview(button)
        self.button = button
        
        button.translatesAutoresizingMaskIntoConstraints = false
        view.bottomAnchor.constraint(equalTo: button.bottomAnchor, constant: 150).isActive = true
        view.centerXAnchor.constraint(equalTo: button.centerXAnchor, constant: 0).isActive = true
        
        self.view = view
    }
    
    override func viewWillAppear(_ animated: Bool) {
        super.viewWillAppear(animated)
        
        intValueObserver = self.observe(\.model.intValue, options: [.initial, .new], changeHandler: { mySelf, change in
            mySelf.updateLabel()
        })
    }
    
    override func viewWillDisappear(_ animated: Bool) {
        intValueObserver = nil
        
        super.viewWillDisappear(animated)
    }
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()

final class MyModel: NSObject {
    @objc dynamic var intValue: Int = 0
    
    func increment() {
        intValue += 1
    }
}

Hi thank you for this, I will try it out