When you streamed down the spreadsheet to the user, did you call Response.End() afterwards? If you didn't, all of the page will get appended to the output stream and get stuck on the end of the document.

I'd not normally use they RenderControl() method to get the data, as it would give you the entire web control, and presumably you'd need to parse/transform the resulting HTML into CSV format? Normally I'd use the underlying data source, and have a function that turns that into the data. Here's a basic example function that turns a recordset into a CSV file and streams it to the browser:

protected void btnDownload_Click(object sender, EventArgs e)
        {
            //get the list of data from data access class
            SqlDataReader dr = TestData.GetExportData();

            //loop through and format
            StringBuilder sb = new StringBuilder();
            int maxFields = dr.FieldCount;

            //build the csv string

            //add headers
            for (int x = 0; x < maxFields; x++)
            {
                sb.AppendFormat("\"{0}\"", dr.GetName(x));
                if (x < maxFields - 1)
                {
                    sb.Append(",");
                }
                else
                {
                    sb.Append("\r\n");
                }
            }

            System.Globalization.CultureInfo cultureInfo = System.Globalization.CultureInfo.InvariantCulture;

            //add data
            while (dr.Read())
            {
                for (int x = 0; x < maxFields; x++)
                {
                    sb.AppendFormat("\"{0}\"", dr[x].ToString());
                    if (x < maxFields - 1)
                    {
                        sb.Append(",");
                    }
                    else
                    {
                        sb.Append("\r\n");
                    }
                }
            }

            string exportData = sb.ToString();

            dr.Close();

            //send the csv to the user
            string fileName = "attachment; filename=my_csv_file.csv";

            Response.ContentType = "application/octet-stream";
            Response.AddHeader("Content-Disposition", fileName);
            Response.Write(exportData);
            Response.End();
        }

Hi Tim,

Thanks for your response. I did eventually get it to render the gridview properly but I wasn't quite sure why my solution worked. Basically I had to include:

Tabpage tp = (TabPage)this.Parent;
foreach (Control c in tp.Controls)
{
  c.Controls.Clear();
} 

This seemed to clear out the excess controls before I called GridView.RenderControl();

But in answer to your question, yes I did call Response.End(); which is why I'm confused. Also it wasn't my intention to export the data as a csv file. The client insisted on having the spreadsheet render the table so I had to do things a little differently.

Anyway thanks again for the help :-) 

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