快捷键盘高度返回0

Question

单击按钮时，我的代码第一次运行正常，但我得到了键盘的高度，但问题是当它退出时又再次调用它，它返回hight 0，这是代码的帮助

@IBAction func showCaseProgressSliderBtn(_ sender: Any){
    NotificationCenter.default.addObserver(self, selector: #selector(keyboardWillShow), name: .UIKeyboardWillShow, object: nil)

}

@objc func keyboardWillShow(notification: NSNotification) {
    if let keyboardSize = (notification.userInfo?[UIKeyboardFrameBeginUserInfoKey] as? NSValue)?.cgRectValue {
        let keyboardHeight = keyboardSize.height
        keyboardHeightCG = keyboardHeight
        print("keyboard is \(keyboardHeightCG)")
    }
}

Answer 1

用UIKeyboardFrameEndUserInfoKey检查它怎么办呢？