c＃export to excel file getting error message

Question

I am using Excel 2010 I have the following code that I like to export to a xls file but I am getting the following message:

The file you are trying to open, 'Report.xls', is in a different format than specified by the file extension. Verify that the file is not corrupted and is for the trusted source before opening the file. Do you want to open the file now?

Note that is still opens but not sure why I am getting the message

           ....
            a.Fill(dtRecords);

            Response.ClearContent();
            Response.AddHeader("content-disposition", "attachment;filename=Report.xls");
            Response.ContentType = "application/ms-excel";
            string tab = string.Empty;

            foreach (DataColumn datacol in dtRecords.Columns)
            {
                Response.Write(tab + datacol.ColumnName);
                tab = "\t";
            }
            Response.Write("\n");

            foreach (DataRow dr in dtRecords.Rows)
            {
                tab = "";
                for (int j = 0; j < dtRecords.Columns.Count; j++)
                {
                    Response.Write(tab + Convert.ToString(dr[j]));
                    tab = "\t";
                }

                Response.Write("\n");
            }
            Response.End();

Answer 1

我相信.xls文件的官方mime类型是application/vnd.ms-excel （ source ）

Answer 2

You are getting this message because you are trying to export character separated value (CSV) stream as XLS file.

CSV is textual format, while XLS is complex binary format with much more features than CSV.

MS Excel complains because it first tried to open the file as XLS but it figured out that file is actually not XLS so it shows warning message, but is still smart enough to figure out that file is CSV and act accordingly.

Try saving the file with extension .csv and with content-type text/csv .