export excel problem in asp.net

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ASP.NET

protected void btnExcel_Click(object sender, ImageClickEventArgs e)
{
Response.ClearContent();
Response.Buffer = true;
Response.AddHeader("content-disposition", string.Format("attachment; filename={0}", "Customers.xls"));
Response.ContentType = "application/ms-excel";
StringWriter sw = new StringWriter();
HtmlTextWriter htw = new HtmlTextWriter(sw);
gvdetails.AllowPaging = false;
//Change the Header Row back to white color
gvdetails.HeaderRow.Style.Add("background-color", "#FFFFFF");
//Applying stlye to gridview header cells
for (int i = 0; i < gvdetails.HeaderRow.Cells.Count; i++)
{
gvdetails.HeaderRow.Cells[i].Style.Add("background-color", "#507CD1");
}
int j = 1;
//This loop is used to apply stlye to cells based on particular row
foreach (GridViewRow gvrow in gvdetails.Rows)
{
gvrow.BackColor = Color.White;
if (j <= gvdetails.Rows.Count)
{
if (j % 2 != 0)
{
for (int k = 0; k < gvrow.Cells.Count; k++)
{
gvrow.Cells[k].Style.Add("background-color", "#EFF3FB");
}
}
}
j++;
}
gvdetails.RenderControl(htw);
Response.Write(sw.ToString());
Response.End();
}

i have used this coding ..but it exports not only the Gridview data,it export the form Menu,buttons,everything on the page..

any solutions?