У меня есть четыре текстовых файла, и когда я нажимаю кнопку возврата на клавиатуре iPhone, он не собирается сначала текстовое поле

Question

У меня есть четыре текстовых поля для otp, и когда я нажимаю первый textfield, он переходит к следующему textfeild, а когда я нажимаю backspace на втором textfeild, он должен возвращаться к первому textfeild назад.а оно не идет?

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool
{

    if textField == otpNumberOne || (otpNumberTwo != nil) || (otpNumberThree != nil) || (otpNumberFour != nil)
    {
        guard NSCharacterSet(charactersIn: "0123456789").isSuperset(of: CharacterSet(charactersIn: string)) else
        {
            return false
        }
        let maxLength = 1
        let currentString: NSString = textField.text! as NSString
        let newString: NSString =
            currentString.replacingCharacters(in: range, with: string) as NSString

        if (range.length == 0){
            if textField == otpNumberOne {

                otpNumberTwo?.becomeFirstResponder()
            }
            if textField == otpNumberTwo {

                otpNumberThree?.becomeFirstResponder()
            }
            if textField == otpNumberThree {

                otpNumberFour?.becomeFirstResponder()
            }
            if textField == otpNumberFour {


                otpNumberFour?.resignFirstResponder()

            }
            textField.text? = string

            otp = "\(otpNumberOne.text!)\(otpNumberTwo.text!)\(otpNumberThree.text!)\(otpNumberFour.text!)"


            if otpNumberOne.hasText && otpNumberTwo.hasText && otpNumberThree.hasText && otpNumberFour.hasText
            {
                if vcode == otp
                {
                    if InternetStatusClass.sharedInstance.isConnected == true
                    {
                        self.hud = MBProgressHUD.showAdded(to: UIApplication.shared.keyWindow!, animated: true)

                        self.hud.label.text = "Loading..."

                        executeVerifyMobileServerAPI()

                    }
                    else
                    {
                        let alertController = UIAlertController(title: "Error", message: "No connection", preferredStyle: .alert)

                        let defaultAction = UIAlertAction(title: "OK", style: .cancel, handler: nil)
                        alertController.addAction(defaultAction)

                        self.present(alertController, animated: true, completion: nil)
                    }

                }
            }

            return false
        }else if (range.length == 1) {

            if textField == otpNumberFour {


                otpNumberThree?.becomeFirstResponder()
            }
            if textField == otpNumberThree {

                otpNumberTwo?.becomeFirstResponder()
            }
            if textField == otpNumberTwo {

                otpNumberOne?.becomeFirstResponder()
            }
            if textField == otpNumberOne {

                otpNumberOne?.resignFirstResponder()
            }
            textField.text? = ""
            return false
        }
       return newString.length <= maxLength

    }
    return true
}