Allowing single digit in UITextField in iOS

Question

I have a Verification ViewController, I get 4 digit verification code by SMS and I need to enter those code to login, I have created the ViewController

Answer 1

Use this code if you don't want to work with tag and it works better then above

func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
        // On inputing value to textfield
        if ((textField.text?.characters.count)! < 1  && string.characters.count > 0){
            if(textField == txtOne)
            {
                txtTwo.becomeFirstResponder()
            }
            if(textField == txtTwo)
            {
                txtThree.becomeFirstResponder()
            }
            if(textField == txtThree)
            {
                txtFour.becomeFirstResponder()
            }

            textField.text = string
            return false
        }
        else if ((textField.text?.characters.count)! >= 1  && string.characters.count == 0){
            // on deleting value from Textfield
            if(textField == txtTwo)
            {
                txtOne.becomeFirstResponder()
            }
            if(textField == txtThree)
            {
                txtTwo.becomeFirstResponder()
            }
            if(textField == txtFour)
            {
                txtThree.becomeFirstResponder()
            }
            textField.text = ""
            return false
        }
        else if ((textField.text?.characters.count)! >= 1  )
        {
            textField.text = string
            return false
        }
        return true
    }