How to code DropdownList.DataTextField/DataValueField, so that the users can click a DDL item to open a file

In the following codes, I tried to insert  the file names of a folder = Request.QueryString("folder")
to a DropdownList control.  The dirInfo.GetFiles is utilized as the DDL DataSource successfully.
However, the DDL just display the file names as text strings, not as a hyperlink list.  How
can I define
                   DropDownList1.DataTextField = ?
                   DropDownList1.DataValueField = file.Nameames are not
so that the users can click a DDL item to open the file?


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        Dim folder As String = Nothing
        folder = Request.QueryString("folder")
      &nb ...