iOS. Изменение положения элементов при отображении/скрытии клавиатуры

KeyboardEventsViewController.swift

import UIKit

class ViewController: UIViewController {
    @IBOutlet weak var bottomConstraint: NSLayoutConstraint!
    let desirableBottomPadding: CGFloat = 16.0

    override func viewDidLoad() {
        super.viewDidLoad()
        
        NotificationCenter.default.addObserver(self, selector: #selector(onKeyboardWillShow(_:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
        NotificationCenter.default.addObserver(self, selector: #selector(onKeyboardWillHide(_:)), name: NSNotification.Name.UIKeyboardWillHide, object: nil)
        
        bottomConstraint.constant = desirableBottomPadding
    }
    
    deinit {
        NotificationCenter.default.removeObserver(self)
    }
    
    @IBAction func onEditFinished(_ sender: UITextField) {
        sender.resignFirstResponder()
    }
    
    func onKeyboardWillShow(_ notification: Notification) {
        let keyboardSize = notification.userInfo!["UIKeyboardFrameEndUserInfoKey"] as! CGRect
        bottomConstraint.constant = desirableBottomPadding + keyboardSize.height
    }
    
    func onKeyboardWillHide(_ notification: Notification) {
        bottomConstraint.constant = desirableBottomPadding
    }
}