Gridview Excel Export In C#

void             BindGrid()
{

 DataSet objds = "";
           GridView1.DataSource = objds;
            GridView1.DataBind();
}

void ExcelExport
{
Response.ClearContent();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "UserDetails.xls"));
            Response.ContentType = "application/ms-excel";
            StringWriter sw = new StringWriter();
            HtmlTextWriter htw = new HtmlTextWriter(sw);
            gvAdminDetails.AllowPaging = false;
            BindGrid();
            //Change the Header Row back to white color
            Gridview1.HeaderRow.Style.Add("background-color", "#FFFFFF");

            //Applying stlye to gridview header cells
            for (int i = 0; i < gvAdminDetails.HeaderRow.Cells.Count; i++)
            {
               Gridview1.HeaderRow.Cells[i].Style.Add("background-color", "#F0F0F0");
            }
            int j = 1;
            //This loop is used to apply stlye to cells based on particular row
            foreach (GridViewRow gvrow in gvAdminDetails.Rows)
            {
                gvrow.BackColor = System.Drawing.Color.White;
                if (j <= Gridview1.Rows.Count)
                {
                    if (j % 2 != 0)
                    {
                        for (int k = 0; k < gvrow.Cells.Count; k++)
                        {
                            gvrow.Cells[k].Style.Add("background-color", "#F0F0F0");
                        }
                    }
                }
                j++;
            }

           Gridview1.RenderControl(htw);
            Response.Write(sw.ToString());

           Gridview1.AllowPaging = true;
            Response.End();
}


public override void VerifyRenderingInServerForm(Control control)
    {
        //required to avoid the runtime error "
        //Control 'GridView1' of type 'GridView' must be placed inside a form tag with runat=server."
    }