HTML ExportToExcel Button - html

Question

I have an ExportToExcel button in my application which is seen all the time. I want this to be changed to be shown only after I click submit and the result is shown.
Here is the code:
<asp:Button ID="btnExport" runat="server" Text="Export To Excel" OnClick = "ExportToExcel" />
protected void ExportToExcel(object sender, EventArgs e)
{
Response.Clear();
Response.Buffer = true;
Response.ContentType = "text/xls";
Response.AddHeader("content-disposition", "attachment;filename=HistoricalReporting.xls");
Response.Charset = "";
using (StringWriter sw = new StringWriter())
{
HtmlTextWriter hw = new HtmlTextWriter(sw);
//To Export all pages
GridView1.AllowPaging = false;
this.BindGridView();
GridView1.HeaderRow.BackColor = Color.White;
foreach (TableCell cell in GridView1.HeaderRow.Cells)
{
cell.BackColor = GridView1.HeaderStyle.BackColor;
}
foreach (GridViewRow row in GridView1.Rows)
{
row.BackColor = Color.White;
foreach (TableCell cell in row.Cells)
{
if (row.RowIndex % 2 == 0)
{
cell.BackColor = GridView1.AlternatingRowStyle.BackColor;
}
else
{
cell.BackColor = GridView1.RowStyle.BackColor;
}
cell.CssClass = "textmode";
}
}
GridView1.RenderControl(hw);
//style to format numbers to string
string style = #"<style> .textmode { } </style>";
Response.Write(style);
Response.Output.Write(sw.ToString());
Response.Flush();
Response.End();
}
}
public override void VerifyRenderingInServerForm(Control control)
{
/* Verifies that the control is rendered */
}