export excel file using gridview in asp.net using vb.net

Hi i am creating excle file inside the for loop :- using below code

GridView1.DataBind()

GridView1.DataSource = dt1

GridView1.DataBind()

Dim path As String = Server.MapPath("~/" & (ConfigurationSettings.AppSettings("DocketAnnexure")))

If Not Directory.Exists(path) Then

Directory.CreateDirectory(path)

End If

If File.Exists(path & "/Invoice_Annexure_details" & awbno + "_" + Convert.ToString(count) & ".xls") Then

File.Delete(path & "/Invoice_Annexure_details" & awbno + "_" + Convert.ToString(count) & ".xls")

End If

Using sw As New StringWriter()

Using hw As New HtmlTextWriter(sw)

Dim writer As StreamWriter = File.CreateText(path & "/Invoice_Annexure_details" & awbno + "_" + Convert.ToString(count) & ".xls")

Try

GridView1.RenderControl(hw)

writer.WriteLine(sw.ToString())

writer.Flush()

writer.Close()

''hw.Flush()

''hw.Close()

''hw.Dispose()

writer.Dispose()

sw.Flush()

sw.Close()

sw.Dispose()

GC.Collect()

Catch ex As Exception

writer.Flush()

writer.Close()

'hw.Flush()

'hw.Close()

'hw.Dispose()

writer.Dispose()

sw.Flush()

sw.Close()

sw.Dispose()

GC.Collect()

End Try

End Using

my first file as been created with data but when i create next file its blank creat