开发需求：对键盘弹出及隐藏事件进行监听

需要通过NotificationCenter对键盘事件进行监听

//键盘即将弹出
        NotificationCenter.default.addObserver(self,selector: #selector(self.keyboardShow(note:)),name: NSNotification.Name.UIKeyboardWillShow,object: nil)
        //键盘即将隐藏
        NotificationCenter.default.addObserver(self,selector: #selector(self.keyboardHidden(note:)),name: NSNotification.Name.UIKeyboardWillHide,object: nil)

      //键盘弹出监听
    @objc func keyboardShow(note: Notification)  { guard let userInfo = note.userInfo else {return}
        guard let keyboardRect = userInfo[UIKeyboardFrameEndUserInfoKey] as? CGRect else{return}
        //获取键盘弹起的高度
        let keyboardTopYPosition = SCREENHEIGHT - keyboardRect.height

    }

    //键盘隐藏监听
    @objc func keyboardHidden(note: Notification){ }

    //取消键盘监听
    deinit { NotificationCenter.default.removeObserver(self) }

如果要监听键盘完全弹起或隐藏后进行操作，则使用

//注意，这里使用的是UIKeyboardDidShow
        NotificationCenter.default.addObserver(self,name: NSNotification.Name.UIKeyboardDidShow,object: nil)

        //注意，这里使用的是UIKeyboardDidHide
        NotificationCenter.default.addObserver(self,name: NSNotification.Name.UIKeyboardDidHide,object: nil)