How to fix this issues unknown error show at this page - flutter

Question

code for api_addEvent.dart
class ApiAddEventToCalender {
Future<ApiResponseData> addEventToCalender(
String token,
String date,
String time,
String previousEventDocID,
int eventDateEpocMilisecond) async {
ApiResponseData apiResponseData =
ApiResponseData(responseCode: "27", responseMsg: "Unknown Error");
var url = '${Constants.apiEndPoint}/addEventToCalender';
if (date.length < 1) {
ApiResponseData apiResponseData =
ApiResponseData(responseCode: "17", responseMsg: "Invalid date.");
return apiResponseData;
}
if (eventTitle.text.length < 1) {
ApiResponseData apiResponseData = ApiResponseData(
responseCode: "17", responseMsg: "Event title is required.");
return apiResponseData;
}
if (eventString.text.length < 1) {
ApiResponseData apiResponseData = ApiResponseData(
responseCode: "17", responseMsg: "Event description is required.");
return apiResponseData;
}
Map data = {
"Token": token,
"API": "AddEventToCalender",
"Data": {
"tokenType": "jwt",
"date": date,
"title": eventTitle.text,
"event": eventString.text,
"time": time,
"eventDateEpocMilisecond": eventDateEpocMilisecond
}
};
if (previousEventDocID.length > 10) {
data = {
"Token": token,
"API": "AddEventToCalender",
"Data": {
"tokenType": "jwt",
"date": date,
"title": eventTitle.text,
"event": eventString.text,
"time": time,
"eventDateEpocMilisecond": eventDateEpocMilisecond,
"previousEventDocID": previousEventDocID,
}
};
}
//encode Map to JSON
var body = json.encode(data);
var response = await http.post(Uri.parse(url),
headers: {"Content-Type": "application/json"}, body: body);
if (response.statusCode == 200) {
var result = json.decode(response.body.toString());
if (result['ResponseCode'] == "0") {
/*ApiResponseData(
responseCode: "17", responseMsg: 'Event added to calender.');
return apiResponseData; */
} else if (result['ResponseCode'] == "1") {
apiResponseData.responseCode = result['ResponseCode'].toString();
apiResponseData.responseMsg = result['ResponseMsg'].toString();
return apiResponseData;
}
}
return apiResponseData;
}
}
2nd code for call api_addEvent.dart
Future<void> _addEventToCalender(String date, String time,
int eventDateEpocMilisecond, String previousEventDocID) async {
setState(() {
_progressBarActive = true;
});
var result = await ApiAddEventToCalender().addEventToCalender(
widget.token, date, time, previousEventDocID, eventDateEpocMilisecond);
if (result.responseCode == "0") {
} else {
if (result.responseCode == "1") {
Navigator.of(context).pushNamedAndRemoveUntil(
'/social_signin', (Route<dynamic> route) => false);
} else {
showMessageDialogBox(context, result.responseMsg.toString());
}
}
setState(() {
_progressBarActive = false;
});
}
I want to ask how to fix this error message. I tried to fix it but still had no success. For example ApiResponseData (
responseCode: "17", responseMsg: "Event title is required."); will appear the message "Event title is required." if I do not enter a title. But for unknown errors, I'm not sure I should always show near this page. Can someone help me?