How to make correct date format when writing data to Excel

Question

Iam exporting a DataTable to an Excel-file using office interop. The problem is, that Excel does not recognize dates as such, but instead it displays numbers. In another cas

Answer 1

I know this question is old but populating Excell Cells with Dates via VSTO has a couple of gotchas.

• Formatting the entire column did NOT work for me.

• Not even this approach from Microsoft worked: http://msdn.microsoft.com/en-us/library/microsoft.office.tools.excel.namedrange.numberformat.aspx

I found Formula's don't work on dates with yyyy-mmm-dd format - even though the cells were DATE FORMAT! You have to translate Dates to a dd/mm/yyyy format for use in formula's.

For example the dates I am getting come back from SQL Analysis Server and I had to flip them and then format them:

using (var dateRn = xlApp.Range["A1"].WithComCleanup())
{
    dateRn.Resource.Value2 = Convert.ToDateTime(dateRn.Resource.Value2).ToString("dd-MMM-yyyy");
}


using (var rn = xlApp.Range["A1:A10"].WithComCleanup())
{
    rn.Resource.Select();
    rn.Resource.NumberFormat =  "d-mmm-yyyy;@";
}

Otherwise formula's using Dates doesn't work - the formula in cell C4 is the same as C3: