create Excel file

http://www.codepal.co.uk/show/Line_breaks_lost_and_br_tags_show_when_exporting_to_Excel_file

 Protected Sub Page_Load(sender As Object, e As System.EventArgs) Handles Me.Load

    Dim dt As New DataTable
    dt.Columns.Add(New DataColumn("Text1", GetType(System.String)))

    Dim dr As DataRow = dt.NewRow
    dr.Item("Text1") = String.Format("This is line one{0}This is line two{0}This is line three", "<br/>")
    dt.Rows.Add(dr)

    Response.Clear()
    Response.AddHeader("content-disposition", "attachment;filename=exported.xls")
    Response.AddHeader("Pragma", "public")
    Response.AddHeader("Cache-Control", "max-age=0")
    Response.ContentType = "application/vnd.ms-excel"
    Response.ContentEncoding = System.Text.Encoding.UTF8

    Dim gvEx As New GridView
    gvEx.AutoGenerateColumns = True
    gvEx.AllowSorting = False
    gvEx.AllowPaging = False
    Dim sw As New System.IO.StringWriter
    Dim hw As New System.Web.UI.HtmlTextWriter(sw)
    gvEx.DataSource = dt
    gvEx.DataBind()
    hw.AddAttribute("xmlns:x", "urn:schemas-microsoft-com:office:excel") ' optional'
    hw.RenderBeginTag(HtmlTextWriterTag.Html)
    hw.RenderBeginTag(HtmlTextWriterTag.Head)
    hw.RenderBeginTag(HtmlTextWriterTag.Style)
    hw.Write("br {mso-data-placement:same-cell;}")
    hw.RenderEndTag() ' /Style'
    hw.RenderEndTag() ' /Head'
    hw.RenderBeginTag(HtmlTextWriterTag.Body)
    gvEx.RenderControl(hw)
    hw.RenderEndTag() ' /Body'
    hw.RenderEndTag() ' /Html'
    Response.Write(HttpUtility.HtmlDecode(sw.ToString))    ' turns &lt;br/&gt; back into <br/>'
    Response.Flush()
    Response.End()

End Sub