格式异常：字符串未被识别为有效的日期时间

Question

My code works fine as far as I give the values for Begin date and enddate. However, when they are null values, it returns the format exception. This is what I did:

public static string CheckInsertRecord(String EventType, String BeginDate, String EndDate) 
{
    NCDCPoint ncdc = new NCDCPoint();
    CEOSurveyDataContext CDC = new CEOSurveyDataContext();
    int et = Convert.ToInt32(EventType);
    CultureInfo provider = CultureInfo.InvariantCulture;
    DateTime b = Convert.ToDateTime(BeginDate);
    DateTime e = Convert.ToDateTime(EndDate);

    var query = (from n in CDC.NCDCPoints
                where n.EVENT_TYPE_ID == et && n.BeginDate == b && n.EndDate == e
                select new { 
                   n.EVENT_TYPE_ID,
                   BeginDate =  n.BeginDate.ToString("yyyy-MM-dd",provider),
                   EndDate = n.EndDate.ToString(),
                   n.BeginLATLONG,
                   n.EndLATLONG
                });
   if (query.Any())
   {
       return new JavaScriptSerializer().Serialize(query.ToList());
   }
   else
   {
       return "No duplicate";
   }
}

Putting try and catch was not useful as I cannot access the return values. Can u please let me know how to deal with this error.

Answer 1

You could check to see if the strings are null before trying to convert them to DateTimes

if (BeginDate == null || EndDate == null) {
    // handle it appropriately, perhaps by setting a default or returning
}

DateTime b = Convert.ToDateTime(BeginDate);
DateTime e = Convert.ToDateTime(EndDate);

If possible, you could also change your method to accept DateTime values instead of strings

Answer 2

DateTime is not nullable. So trying to format a string that is Null or Empty should return an exception.

public static string CheckInsertRecord(String eventType, String beginDate, String endDate)
{
    NCDCPoint ncdc = new NCDCPoint();
    CEOSurveyDataContext CDC = new CEOSurveyDataContext();
    int et = Convert.ToInt32(eventType);
    CultureInfo provider = CultureInfo.InvariantCulture;

    String queryBeingDate = string.Empty;
    String queryEndDate = string.Empty;
    DateTime beginDateTime;
    DateTime endDateTime;
    if (DateTime.TryParse(beginDate, out beginDateTime))
    {
       queryBeingDate = beginDateTime.ToString("yyyy-MM-dd");
    }

    if(DateTime.TryParse(endDate, out endDateTime))
    {
       queryEndDate = endDate;
    }

    var query = (from n in CDC.NCDCPoints
                 where n.EVENT_TYPE_ID == et && n.BeginDate == b && n.EndDate == e
                 select new
                 {
                     n.EVENT_TYPE_ID,
                     BeginDate = queryBeingDate,
                     EndDate = queryEndDate,
                     n.BeginLATLONG,
                     n.EndLATLONG
                 });
}

Answer 3

You never said what your string values were. Are they in the right format?

Put your try/catch routine like this:

void test(string BeginDate, string EndDate) {
  DateTime noDate = new DateTime(1900, 1, 1);
  DateTime b;
  DateTime e;
  try {
    b = Convert.ToDateTime(BeginDate);
  } catch (Exception error) {
    b = noDate;
    MessageBox.Show("Invalid Format: " + BeginDate);
  }
  try {
    e = Convert.ToDateTime(EndDate);
  } catch (Exception error) {
    e = noDate;
    MessageBox.Show("Invalid Format: " + EndDate);
  }
  if (e < b) {
    throw new Exception("End Date can not be before Begin Date.");
  }
}

Answer 4

You can potentially change the DateTime to Nullable, DateTime? or check the strings you're passing in with string.IsNullOrEmpty() and add whatever logic you think's best to handle null values.

Answer 5

Use DateTime.TryParse() instead of Convert.ToDateTime(). That never throws an exception and returns a bool to tell you if the conversion worked.

Answer 6

substitute

 DateTime b = Convert.ToDateTime(BeginDate);
    DateTime e = Convert.ToDateTime(EndDate);

with

 DateTime b, e;
  if(!DateTime.TryParse(BeginDate,out b))
      b = YOurDefaultBeginDate;
  if(!DateTime.TryParse(EndDate,out e))
      e = YOurDefaultEndDate;