Dim doc As New PrintDoc
Dim rt As New Prt.RenderTable
Dim rx As prt.RenderText
Dim cnt As Integer
Dim tbl As Table = Tables("订单")
Dim drs As List(Of DataRow)
Dim pds As List(Of String) = tbl.DataTable.GetValues("产品",tbl.Filter)
rt.Style.GridLines.All = New prt.LineDef(0.3,Color.LightGray)
rt.CellStyle.Spacing.All = 1
rt.Style.Font = tbl.Font
For c As Integer = 0 To tbl.Cols.Count - 1 '生成列标题
    rt.Cells(0,c).Text = tbl.Cols(c).Name
    rt.Cols(c).Width = tbl.Cols(c).PrintWidth
Next
For Each pd As String In pds '分产品打印
    If tbl.Filter > "" Then
        drs = tbl.DataTable.Select("产品 = '" & pd & "' And " & tbl.Filter)
    Else
        drs = tbl.DataTable.Select("产品 = '" & pd & "'" )
    End If
    For Each dr As DataRow In drs '逐行打印此产品的订单
        cnt = rt.Rows.Count
        For c As Integer = 0 To tbl.Cols.Count - 1
            rt.Cells(cnt, c).Text = dr(tbl.Cols(c).Name)
        Next
    Next
    cnt = rt.Rows.Count
    rt.Cells(cnt, 0).Text = "小计 " & pd '打印产品的小计
    rt.Cells(cnt,5).Text = tbl.compute("Sum(数量)", "产品 = '" & pd & "'")
Next
cnt = rt.Rows.Count
rt.Cells(cnt, 0).Text = "合计 " '打印合计
rt.Cells(cnt, 5).Text = tbl.compute("Sum(数量)")
doc.Body.Children.Add(rt)
doc.preview()

代码说明：

上面的代码中，每次要打印一个新行，都先通过下面的代码获得已经打印的行数，并保存在变量cnt中：

cnt = rt.Rows.Count

假定已经打印了9行，编号为0到8，执行上面的代码，cnt的值就等于9。
显然下一个订单或小计，应该打印在编号为9的行，也就是编号为cnt的行。