when need to disable the button on the alert viewController.

Alert button disable

// another solution of disabling the button 
//where alert is variable in class 
    override func textField(_ textField: UITextField,
                            shouldChangeCharactersIn range: NSRange,
                            replacementString string: String) -> Bool {
        if range.location >= 1 { return true } // if we have one or more characters

        guard let isTextFieldEmpty = textField.text?.isEmpty else { return true }

        if !isTextFieldEmpty {
            alert?.actions.first?.isEnabled = false
        } else {
            alert?.actions.first?.isEnabled = true
        }
        return true
    }