Exporting Page content Excel in asp.net where data is generated dynamically

protected void btnExcel_Click(object sender, ImageClickEventArgs e)
        {
            GenerateExcel(GridView);
        }

public static void GenerateExcel(GridView gv)
        {
            HttpContext.Current.Response.Clear();
            HttpContext.Current.Response.AppendHeader("Content-disposition", "attachment; filename=Leave_Report.xls");
            HttpContext.Current.Response.ContentType = "application/ms-excel";

            using (StringWriter sw = new StringWriter())
            {
                using (HtmlTextWriter htw = new HtmlTextWriter(sw))
                {
                    //  Create a table to contain the grid
                    Table table = new Table();

                    //  include the gridline settings
                    table.GridLines = gv.GridLines;

                    //  add the header row to the table
                    if (gv.HeaderRow != null)
                    {
                        PrepareControlForExport(gv.HeaderRow);
                        table.Rows.Add(gv.HeaderRow);
                    }
                    //Make Header Coloruful

                    for (int j = 0; j < gv.Columns.Count; j++)
                    {
                        //Apply style to Individual Cells
                        gv.HeaderRow.Cells[j].Style.Add("background-color", "#4DB4EE");

                    }

                    //  add each of the data rows to the table
                    foreach (GridViewRow row in gv.Rows)
                    {
                        PrepareControlForExport(row);
                        table.Rows.Add(row);
                    }

                    //  add the footer row to the table
                    if (gv.FooterRow != null)
                    {
                        PrepareControlForExport(gv.FooterRow);
                        table.Rows.Add(gv.FooterRow);
                    }

                    //  render the table into the htmlwriter
                    table.RenderControl(htw);

                    //  render the htmlwriter into the response
                    HttpContext.Current.Response.Write(sw.ToString());
                    HttpContext.Current.Response.End();
                }
            }


        }
        private static void PrepareControlForExport(Control control)
        {
            for (int i = 0; i < control.Controls.Count; i++)
            {
                Control current = control.Controls[i];
                if (current is LinkButton)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as LinkButton).Text));
                }
                else if (current is ImageButton)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as ImageButton).AlternateText));
                }
                else if (current is HyperLink)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as HyperLink).Text));
                }
                else if (current is DropDownList)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as DropDownList).SelectedItem.Text));
                }
                else if (current is CheckBox)
                {
                    control.Controls.Remove(current);
                    control.Controls.AddAt(i, new LiteralControl((current as CheckBox).Checked ? "True" : "False"));
                }

                if (current.HasControls())
                {
                    PrepareControlForExport(current);
                }
            }
        }
public override void VerifyRenderingInServerForm(Control control)
        {
            /* Verifies that the control is rendered */
        }