Convert.ToDateTime('Datestring') 到所需的 dd-MMM-yyyy 日期格式

Question

I'm trying to export to excel I have string of Date which can be in any format of date but I wanted to convert it to dd-MMM-yyyy format. I have tried every Convert.ToDatetime option which converts only to the System format. I want it to convert dd-MMM-yyyy format.

Thanks Inadvance.

List<UnavailableModel> collection = UnavailableBL.GetAllUnavailableDetails(FilteredFacetsJsonString).Result.ToList();
base.Warning(string.Format("Get {0} number of records ", collection.Count));
List<object> obj = new List<object>();
obj.Insert(0, new string[7] { "NAME", "REGION NAME", "MANAGER NAME", "FROM DATE", "TO DATE", "CATEGORY", "COMMENTS" });

int count = 1;
foreach (var audit in collection)
{
    DateTime? dt1 = null, dt2 = null;
    string StartDate = null, EndDate = null;
    if (audit.FromDate != null)
    {
        dt1 = Convert.ToDateTime(audit.FromDate);
        StartDate = dt1.ToString().Substring(0, 10);
    }
    if (audit.ToDate != null)
    {
        dt2 = Convert.ToDateTime(audit.ToDate);
        EndDate = dt2.ToString().Substring(0, 10);
    }
    obj.Insert(count, new string[7]{
        string.Format("\"{0}\"", audit.Region_Name),
        string.Format("\"{0}\"",  audit.First_Name+" 
        "+audit.Last_Name),
        string.Format("\"{0}\"", audit.Manager_First_Name+" "+audit.Manager_Last_Name),
        string.Format("\"{0}\"", StartDate),
        string.Format("\"{0}\"", EndDate),
        string.Format("\"{0}\"", audit.Category),
        string.Format("\"{0}\"", audit.Comments)
    });
    count++;
}
base.Warning(string.Format("Data table created "));


for (int i = 0; i < obj.Count; i++)
{
   string[] stringCSV = (string[])obj[i];
   for (int j = 0; j < stringCSV.Length; j++)
   {
       //Append data with separator.
       sb.Append(stringCSV[j] + ',');
   }

   //Append new line character.
   sb.Append("\r\n");

}

Answer 1

First, a DateTime has no format . It is stored internally as an integer representing the number of ticks since 1/1/0001. A DateTime only "has a format" when displayed . And that's only after it's been converted to a string (whether by using the default formatting of the current culture or one you specify explicitly when calling ToString ).

Second, this line is pointless:

dt1 = Convert.ToDateTime(audit.FromDate);`

As FromDate is already a DateTime , all you would need to do is assign it directly :

dt = audit.FromDate;

But you're mixing things up. You cannot assign a formatted Date (a string ) to a DateTime variable. Format your Date as a string and store it as a string variable and pass that to your Excel building method:

string EndDate = audit.FromDate.ToString("dd-MMM-yyyy");

There is absolutely no need for DateTime.Parse , DateTime.TryParse , DateTime.TryParseExact or Convert.ToDateTime in your code. You have everything you need already without performing any uncecessary "conversions".

Answer 2

If you have the DateTime in hand you can write that as string in excel like below:

StartDate = dt1.ToString("dd-MMM-yyyy");

Then use that string to enter excel.

Answer 3

Just to expand a bit on Afshin's practical solution. There are quite a bit of resources and questions on this problem. Generally, when formatting the string from an object, the ToString method is your friend. In the case of a date, you can pass in the custom format that you want as a string:

StartDate = dt1.ToString("dd-MMM-yyyy");

Keep in mind that it's usually safer to use DateTime.TryParse when dealing with external resources. Here's some guidance on the subject.