dynamic block enter text in textfield delegate

textField+delegate.swift

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

     guard textField == self.exportAmountTextField else { return true }

     let oldString: NSString = (textField.text ?? "") as NSString
     let resultString = oldString.replacingCharacters(in: range, with: string)

     let doubleString = Double(resultString) ?? 0

     if (string.trimmingCharacters(in: CharacterSet.decimalDigits).count == 0 || string == "" || string == ".") == false {
         return false
     }

     if resultString.components(separatedBy: ".").last?.count ?? 7 > 6 {
         return false
     }

     if (doubleString > twipAmount) || (doubleString > Double(99999999)) {
         return false
     }

     return true
 }