Swift - Get height of keyboard

See: https://stackoverflow.com/questions/31774006/how-to-get-height-of-keyboard-swift

import UIKit

class ViewController: UIViewController {

    @IBOutlet weak var textFieldBottomConstraint: NSLayoutConstraint!
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        
        NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow(notification:)), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
        
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

    @objc func keyboardWillShow(notification:NSNotification) {
        
        if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {
            let keyboardHeight = keyboardSize.height
            print(keyboardHeight)
        }
        
        if let info = notification.userInfo {
            
            let rect:CGRect = info["UIKeyboardFrameEndUserInfoKey"] as! CGRect
            
            
            self.view.layoutIfNeeded()
            
            UIView.animate(withDuration: 0.25, animations: {
                
                self.view.layoutIfNeeded()
                self.textFieldBottomConstraint.constant = rect.height + 20
                
            })
            
        }
    }

}