主题：excel格式设置代码，为何不生效呢?

    Dim App As New MSExcel.Application

    App.Visible = False

    Dim Wb As MSExcel.Workbook = App.WorkBooks.Open(flg.filename)

    Dim ws As msexcel.worksheet = wb.worksheets(1)

    Dim rg As msexcel.range  = ws.cells(tb.Rows.Count + hn, tb.Cols.Count)

    With rg.font

        .name = "黑体"

        .size = 9

    End With

    wb.save

    wb.close

    app.quit

导出excel报表后，重新设置他的格式。以上这段代码为何不生效呢，求教。