UItextfield编辑和响应

嗨,问题是我已经将UItextfield设置为有限字符,但它可以与iPhone键盘和Mac键盘配合使用,但当我使用UIView上的数字时,它超过了限制

限制代码:

    import UIKit

class ViewController: UIViewController, UITextFieldDelegate {

    @IBOutlet weak var textField1: UITextField!

    @IBAction func Botton1(_ sender: UIButton) {

        textField1.text = textField1.text! + String (sender.tag)
    }


    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view, typically from a nib.
    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }



    func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        if range.length + range.location > (textField1.text?.count)!{

            return false
        }
        let NewLength = (textField1.text?.count)! + string.count - range.length

        return NewLength < 4
    }


}