Border not showing in excel after exporting in ASP.Net

Question

My code is here . I am exporting excel sheet by using this code but cell borders are not showing in my excel sheet:

 

Private Sub ExportGridToExcel()

Response.Clear()

Response.Buffer = True

Response.ClearContent()

Response.ClearHeaders()

Response.Charset = ""

Dim FileName As String = "Vithal" + DateTime.Now + ".xls"

Dim strwritter As New StringWriter()

Dim htmltextwrtter As New HtmlTextWriter(strwritter)

Response.Cache.SetCacheability(HttpCacheability.NoCache)

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

Response.AddHeader("Content-Disposition", Convert.ToString("attachment;filename=") & FileName)

GridViewBillReport.GridLines = GridLines.Both

GridViewBillReport.HeaderStyle.Font.Bold = True

GridViewBillReport.RenderControl(htmltextwrtter)

Response.Write(strwritter.ToString())

Response.[End]()

End Sub

 

My Excel sheet and my GridView Screenshot are here: