let maxLength = 30
func textField(_ textField: UITextField, shouldChangeCharactersIn range: NSRange, replacementString string: String) -> Bool {
    guard let textFieldText = textField.text,
          let rangeOfTextToReplace = Range(range, in: textFieldText) else {
        return false
    }
    let substringToReplace = textFieldText[rangeOfTextToReplace]
    let count = textFieldText.count - substringToReplace.count + string.count
    return count <= maxLength
}