ChatViewController.swift

@IBOutlet weak var bottomConstraint: NSLayoutConstraint!


override func viewDidLoad() {
   super.viewDidLoad()


   ...


   NotificationCenter.default.addObserver(self, selector: #selector(ChatViewController.keyboardWillShow), name: UIResponder.keyboardWillShowNotification, object: nil)
   NotificationCenter.default.addObserver(self, selector: #selector(ChatViewController.keyboardWillHide), name: UIResponder.keyboardWillHideNotification, object: nil)
   textField.becomeFirstResponder()
}


@objc func keyboardWillShow(notification: NSNotification) {
   guard let userInfo = notification.userInfo else { return }
   guard let keyboardSize = userInfo[UIResponder.keyboardFrameEndUserInfoKey] as? NSValue else { return }


   let keyboardFrame = keyboardSize.cgRectValue


   bottomConstraint.constant = 20 + keyboardFrame.height
}


@objc func keyboardWillHide(notification: NSNotification) {
   bottomConstraint.constant = 60
}