export to excel is not exporting all rows of gridview

gv_tours.DataSource = GetDataTable("select tour_id,tour_leg_id,tour_title,client,distance from uvw_client_visit where company_id=" & company_id & " and employee_id=" & employee_id & " and date_in>='" & sFromDate & "' and date_in<='" & sToDate & "' order by tour_id desc")

gv_tours.DataBind()

Protected Sub gvtours_RowCreated(sender As Object, e As GridViewRowEventArgs)

If gv_tours.DataSource IsNot Nothing Then

subTotal = 0

If e.Row.RowType = DataControlRowType.DataRow Then

Dim dt As DataTable = TryCast(e.Row.DataItem, DataRowView).DataView.Table

Dim tourId As Integer = Convert.ToInt32(dt.Rows(e.Row.RowIndex)("tour_id"))

'total += Convert.ToDecimal(dt.Rows(e.Row.RowIndex)("Price"))

If tourId <> currentId Then

If e.Row.RowIndex > 0 Then

For i As Integer = subTotalRowIndex To e.Row.RowIndex - 1

subTotal += Convert.ToDecimal(gv_tours.Rows(i).Cells(4).Text)

Next

Me.AddTotalRow("Total KM", subTotal.ToString("N2"))

subTotalRowIndex = e.Row.RowIndex

End If

currentId = tourId

End If

End If

End If

End Sub

Private Sub AddTotalRow(labelText As String, value As String)

Dim row As New GridViewRow(0, 0, DataControlRowType.DataRow, DataControlRowState.Normal)

row.Cells.AddRange(New TableCell(4) {New TableCell(), New TableCell(), New TableCell(), New TableCell() With {

.Text = labelText,

.HorizontalAlign = HorizontalAlign.Right

}, New TableCell() With {

.Text = value,

.HorizontalAlign = HorizontalAlign.Center

}})

gv_tours.Controls(0).Controls.Add(row)

End Sub

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

For i As Integer = subTotalRowIndex To gv_tours.Rows.Count - 1

subTotal += Convert.ToDecimal(gv_tours.Rows(i).Cells(4).Text)

Next

Me.AddTotalRow("Total KM", subTotal.ToString("N2"))

End Sub

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

'Dim dt As DataTable = TryCast(gv_tours.DataSource, DataTable)

Response.Clear()

Response.Buffer = True

Response.AddHeader("content-disposition",

"attachment;filename=Client Visit Report.xls")

Response.Charset = ""

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

Dim sw As New StringWriter()

Dim hw As New HtmlTextWriter(sw)

For i As Integer = 0 To gv_tours.Rows.Count - 1

'Apply text style to each Row

gv_tours.Rows(i).Attributes.Add("class", "textmode")

Next

gv_tours.RenderControl(hw)

'style to format numbers to string

Dim style As String = ""

Response.Write(style)

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

Response.Flush()

Response.End()

End Sub

Public Overrides Sub VerifyRenderingInServerForm(ByVal control As Control)

'Verifies that the control is rendered

End Sub

Protected Sub gvtours_PageIndexChanging1(sender As Object, e As GridViewPageEventArgs)

gv_tours.PageIndex = e.NewPageIndex

End Sub