//在键盘上添加“完成“按钮
    func addDoneButtonOnKeyboard() {
        let doneToolbar = UIToolbar()
        
        //左侧的空隙
        let flexSpace = UIBarButtonItem(barButtonSystemItem: .flexibleSpace,
                                        target: nil, action: nil)
        //右侧的完成按钮
        let done: UIBarButtonItem = UIBarButtonItem(title: "完成", style: .done,
                                                    target: self,
                                                    action: #selector(doneButtonAction))
        
        var items:[UIBarButtonItem] = []
        items.append(flexSpace)
        items.append(done)
        
        doneToolbar.items = items
        doneToolbar.sizeToFit()
        
        self.input.inputAccessoryView = doneToolbar
    }
    
    //“完成“按钮点击响应
   @objc func doneButtonAction() {
        //收起键盘
        self.input.resignFirstResponder()
        print("您输入的是：\(input.text!)")
    }

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
        input.delegate = self
        
        //在键盘上添加“完成“按钮
        addDoneButtonOnKeyboard()
    }