export data to execl file

protected void btnExport_Click(object sender, EventArgs e)
   {
           string strReport ="Report";
           GetGridDetails(true); // Function to Bind GridView Data
           ExportDataGrid(dgSRDetails, strReport);
   }

 public void ExportDataGrid(DataGrid oGrid, string exportFile)
    {
        
            //Clear the response, and set the content type and mark as attachment
            Response.ClearContent();
            Response.AddHeader("content-disposition", "attachment; filename=\"" + exportFile + "\"");
            Response.ContentType = "application/excel";

            //Clear the character set
            Response.Charset = "";

            //Create a string and Html writer needed for output
            System.IO.StringWriter oStringWriter = new System.IO.StringWriter();
            System.Web.UI.HtmlTextWriter oHtmlTextWriter = new System.Web.UI.HtmlTextWriter(oStringWriter);

            //Clear the controls from the pased grid
            ClearControls(oGrid);

            //Show grid lines
            oGrid.GridLines = GridLines.Both;

            //Color header
            oGrid.HeaderStyle.BackColor = System.Drawing.Color.LightGray;

            //Render the grid to the writer
            oGrid.RenderControl(oHtmlTextWriter);

            Response.Write(oStringWriter.ToString());

            Response.Flush();
            Response.End();
    }

 private void ClearControls(Control control)
    {
        //Recursively loop through the controls, calling this method
        for (int i = control.Controls.Count - 1; i >= 0; i--)
        {
            ClearControls(control.Controls[i]);
        }

        //If we have a control that is anything other than a table cell
        if (!(control is TableCell))
        {
            if (control.GetType().GetProperty("SelectedItem") != null)
            {
                LiteralControl literal = new LiteralControl();
                control.Parent.Controls.Add(literal);
                try
                {
                    literal.Text = (string)control.GetType().GetProperty("SelectedItem").GetValue(control, null);
                }
                catch
                {
                }
                control.Parent.Controls.Remove(control);
            }
            else if (control.GetType().GetProperty("Text") != null)
            {
                LiteralControl literal = new LiteralControl();
                control.Parent.Controls.Add(literal);
                literal.Text = (string)control.GetType().GetProperty("Text").GetValue(control, null);
                control.Parent.Controls.Remove(control);
            }
        }
        return;
    }