先上效果

用到的变量

@IBOutlet weak var textView: UITextView!

 //MARK: 记录UITextView的原始高度
 var textViewHeight: CGFloat!

viewDidLoad

//获取原始位置
textViewHeight = textView.frame.origin.y

//注册监听
NotificationCenter.default.addObserver(self,selector: #selector(handleKeyboardDisShow(notification:)),name: NSNotification.Name.UIKeyboardDidShow,object: nil)

handleKeyboardDisShow

//MARK: 当键盘显示时
    func handleKeyboardDisShow(notification: NSNotification) {
        //得到键盘frame
        let userInfo: NSDictionary = notification.userInfo! as NSDictionary
        let value = userInfo.object(forKey: UIKeyboardFrameEndUserInfoKey)
        let keyboardRec = (value as AnyObject).cgRectValue

        let height = keyboardRec?.size.height

        //让textView bottom位置在键盘顶部
        UITextView.animate(withDuration: 0.1,animations: {
            var frame = self.textView.frame
            frame.origin.y = height!
            self.textView.frame = frame
        })

    }

textFieldShouldReturn

//MARK: 输入框enter回车事件
    func textFieldShouldReturn(_ textField: UITextField) -> Bool {
        textField.resignFirstResponder()

        //让textView bottom位置还原
        UITextView.animate(withDuration: 0.1,animations: {
            var frame = self.textView.frame
            frame.origin.y = self.textViewHeight
            self.textView.frame = frame
        })
        return true
    }

注销监听

deinit {
        //移除监听
        NotificationCenter.default.removeObserver(self)
    }