Regarding Gridview Export

private void ExportGridView()
    {
        string attachment = "attachment; filename=Employee details.xls";
        Response.ClearContent();
        Response.AddHeader("content-disposition", attachment);
        Response.ContentType = "application/ms-excel";
        StringWriter sw = new StringWriter();
        HtmlTextWriter htw = new HtmlTextWriter(sw);
        GridView1.RenderControl(htw);
        Response.Write(sw.ToString());
        Response.End();
    }

public override void VerifyRenderingInServerForm(Control control)
   {
   }

   private void PrepareGridViewForExport(Control gv)
   {
       LinkButton lb = new LinkButton();
       Literal l = new Literal();
       string name = String.Empty;
       for (int i = 0; i < gv.Controls.Count; i++)
       {
           if (gv.Controls[i].GetType() == typeof(LinkButton))
           {
               l.Text = (gv.Controls[i] as LinkButton).Text;
               gv.Controls.Remove(gv.Controls[i]);
               gv.Controls.AddAt(i, l);
           }
           else if (gv.Controls[i].GetType() == typeof(DropDownList))
           {
               l.Text = (gv.Controls[i] as DropDownList).SelectedItem.Text;
               gv.Controls.Remove(gv.Controls[i]);
               gv.Controls.AddAt(i, l);
           }
           else if (gv.Controls[i].GetType() == typeof(CheckBox))
           {
               l.Text = (gv.Controls[i] as CheckBox).Checked ? "True" : "False";
               gv.Controls.Remove(gv.Controls[i]);
               gv.Controls.AddAt(i, l);
           }
           if (gv.Controls[i].HasControls())
           {
               PrepareGridViewForExport(gv.Controls[i]);
           }
       }

protected void Expbtn_Click(object sender, EventArgs e)
    {
        PrepareGridViewForExport(GridView1);
        ExportGridView();

   }