Notification.swift

//: A UIKit based Playground for presenting user interface
  
import UIKit
import PlaygroundSupport

// Define new Notification.Name
extension Notification.Name {
    
    static let ButtonDidTap = Notification.Name(rawValue: "com.vialyx.ButtonDidTap")
    
}

final class MyViewController: UIViewController {
    
    weak var textField: UITextField!
    
    override func loadView() {
        let view = UIView()
        view.backgroundColor = .white
        
        // Add UITextField
        let textField = UITextField()
        textField.frame = CGRect(x: 150, y: 200, width: 200, height: 20)
        textField.placeholder = "will become first respounder"
        textField.textColor = .black
        self.textField = textField
        view.addSubview(textField)
        
        // Add UIButton
        let button = UIButton(type: .custom)
        button.frame = CGRect(x: 0, y: 0, width: 200, height: 20)
        button.setTitle("Tap to post notification", for: UIControl.State())
        button.setTitleColor(.red, for: UIControl.State())
        button.addTarget(self,
                         action: #selector(tap),
                         for: .touchUpInside)
        view.addSubview(button)
        
        self.view = view
    }
    
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // Setup observing
        let notificationCenter = NotificationCenter.default
        notificationCenter.addObserver(self.textField,
                                       selector: #selector(becomeFirstResponder),
                                       name: .ButtonDidTap, object: nil)
    }
    
    @objc private func tap() {
        print("buttonDidTap")
        NotificationCenter.default.post(name: .ButtonDidTap,
                                        object: self)
    }
    
}
// Present the view controller in the Live View window
PlaygroundPage.current.liveView = MyViewController()