Element at the bottom of view disappear after hidi

I have 2 button at the bottom of my screen.I implement the code below in order to show and hide keyboard but do not cover my 2 button at the bottom.

override func viewDidLoad() {
        super.viewDidLoad()

    NotificationCenter.default.addObserver(self, selector: #selector(MyViewController.keyboardWillShow), name: NSNotification.Name.UIKeyboardWillShow, object: nil)
    NotificationCenter.default.addObserver(self, selector: #selector(MyViewController.keyboardWillHide), name: NSNotification.Name.UIKeyboardWillHide, object: nil)

    //here will hide the keyboard when tap the text view 2 times
    let tap = UITapGestureRecognizer(target: self, action: #selector(hideKeyBoard))
    self.statusTextView.addGestureRecognizer(tap)
}

@objc func hideKeyBoard(sender: UITapGestureRecognizer? = nil){
        statusTextView.endEditing(true)
 }

@objc func keyboardWillShow(notification: NSNotification) {
        if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {

            if let window = self.view.window?.frame {
                // We're not just minusing the kb height from the view height because
                // the view could already have been resized for the keyboard before
                self.view.frame = CGRect(x: self.view.frame.origin.x,
                                         y: self.view.frame.origin.y,
                                         width: self.view.frame.width,
                                         height: window.origin.y + window.height - keyboardSize.height)
            }

        }
    }

    @objc func keyboardWillHide(notification: NSNotification) {
        if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {

            let viewHeight = self.view.frame.height
            self.view.frame = CGRect(x: self.view.frame.origin.x,
                                     y: self.view.frame.origin.y,
                                     width: self.view.frame.width,
                                     height: viewHeight + keyboardSize.height)
        }
    }

With the code above,I successfully show and hide the keyboard without cover any element at the bottom.

But strange thing happen,when I tapped the textview 2 times,the keyboard is hide but the 2 button at bottom of screen is disappear.

So my question is,why the element will disappear when hide the keyboard? And how to solve it??

Use UIKeyboardFrameEndUserInfoKey instead of UIKeyboardFrameBeginUserInfoKey as UIKeyboardFrameBeginUserInfoKey can return different values in keyboardWillShow and keyboardWillHide

UIKeyboardFrameBeginUserInfoKey – frame of the keyboard at the beginning of the current keyboard state change. UIKeyboardFrameEndUserInfoKey – frame of the keyboard at the end of the current keyboard state change.