Exporting simple gridview to excel

Question

I have below markup in .aspx  page 

<asp:Button ID="btnExport" runat="server" Text="Export" OnClick = "ExportToExcel" />

and below code behind i am using it runs normally but does not show any exported file

Protected Sub ExportToExcel(sender As Object, e As EventArgs)

Response.Clear()

Response.Buffer = True

Response.AddHeader("content-disposition", "attachment;filename=GridViewExport.xls")

Response.Charset = ""

Response.ContentType = "application/vnd.ms-excel"

Using sw As New StringWriter()

Dim hw As New HtmlTextWriter(sw)

'To Export all pages

grdUserReports.AllowPaging = False

Me.SearchReportUser()

grdUserReports.HeaderRow.BackColor = Color.White

For Each cell As TableCell In grdUserReports.HeaderRow.Cells

cell.BackColor = grdUserReports.HeaderStyle.BackColor

Next

For Each row As GridViewRow In grdUserReports.Rows

row.BackColor = Color.White

For Each cell As TableCell In row.Cells

If row.RowIndex Mod 2 = 0 Then

cell.BackColor = grdUserReports.AlternatingRowStyle.BackColor

Else

cell.BackColor = grdUserReports.RowStyle.BackColor

End If

cell.CssClass = "textmode"

Next

Next

grdUserReports.RenderControl(hw)

'style to format numbers to string

Dim style As String = "<style> .textmode { mso-number-format:\@; } </style>"

Response.Write(style)

Response.Output.Write(sw.ToString())

Response.Flush()

Response.[End]()

End Using

End Sub