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 case I pass a string which it then recognizes as a date. In both cases the data is messed up.

I tried NumberFormat @ which is supposed to store the cell in text format, but it didn't work either.

Application app = new Application();
app.Visible = false;
app.ScreenUpdating = false;
app.DisplayAlerts = false;
app.EnableAnimations = false;
app.EnableAutoComplete = false;
app.EnableSound = false;
app.EnableTipWizard = false;
app.ErrorCheckingOptions.BackgroundChecking = false; 

Workbook wb = app.Workbooks.Add(XlWBATemplate.xlWBATWorksheet);
Worksheet ws = (Worksheet)wb.Worksheets[1];

for (int j = 0; j < dt.Rows.Count; j++)
{
    for (int i = 0; i < dt.Columns.Count; i++)
    {
        Range rng = ws.Cells[j+2, i+1]as Range;
        rng.Value2 = dt.Rows[j][i].ToString();
        rng.NumberFormat = "@";
    }   
}           

wb.SaveAs(filename, Missing.Value, Missing.Value, Missing.Value, Missing.Value,
       Missing.Value, XlSaveAsAccessMode.xlExclusive, Missing.Value, Missing.Value, Missing.Value, Missing.Value, Missing.Value);

wb.Close(false, Missing.Value, Missing.Value);            

app.Workbooks.Close();
app.Application.Quit();
app.Quit();    
System.Runtime.InteropServices.Marshal.ReleaseComObject(ws);
System.Runtime.InteropServices.Marshal.ReleaseComObject(wb);
System.Runtime.InteropServices.Marshal.ReleaseComObject(app);
ws = null;
wb = null;
app = null;
GC.Collect();

Why doesn't my NumberFormat @ work? Shouldn't Textformat display everything the same as I put it in?

Answer 1

Did you try formatting the entire column as a date column? Something like this:

Range rg = (Excel.Range)worksheetobject.Cells[1,1];
rg.EntireColumn.NumberFormat = "MM/DD/YYYY";

The other thing you could try would be putting a single tick before the string expression before loading the text into the Excel cell (not sure if that matters or not, but it works when typing text directly into a cell).