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

Expanding slightly on @Assaf answer, to apply formatting correctly I also had to convert the DateTime via the .ToOADate() function before the formatting took effect. You can do this on a cell by cell basis:

xlWorkSheet.Cells[Row, Col].NumberFormat = ""; // e.g. dd-MMM-yyyy
xlWorkSheet.Cells[Row, Col] = DateTimeObject.ToOADate();

Or you can apply the formatting to the entire column:

xlWorkSheet.Cells[Row, Col].EntireColumn.NumberFormat = ""; // e.g. dd-MMM-yyyy
xlWorkSheet.Cells[Row, Col] = DateTimeObject.ToOADate();