使用treeview在MS Access '10中基于自引用表创建层次结构

Question

我试图按照此微软帖子上的说明操作：http://support.microsoft.com/default.aspx?scid=kb;en-us;209891

基于自引用表创建组织层次结构图表，就像示例一样。我一直收到一个错误，即变量未定义，VBA指向“Optional varReportToID As Variant”行，但是说明说不为此参数提供任何内容。有什么办法可以让代码运行吗？我没有更改代码，我更改了表格上的命名以匹配列出的变量。我在MS Access 2010中工作，但该示例适用于较早版本的MS。

谢谢！

Option Explicit

'=================Load Event for the Form=======================
'Initiates the routine to fill the TreeView control
'============================================================

Public Sub Form_Load()
    Const strTableQueryName = "Employees"
    Dim db As DAO.Database, rst As DAO.Recordset
    Set db = CurrentDb
    Set rst = db.OpenRecordset(strTableQueryName, dbOpenDynaset, dbReadOnly)
    AddBranch rst:=rst, strPointerField:="ReportsTo", strIDField:="EmployeeID",      strTextField:="LastName"
End Sub

'================= AddBranch Sub Procedure ======================
'      Recursive Procedure to add branches to TreeView Control
'Requires:
'   ActiveX Control:  TreeView Control
'              Name:  xTree
'Parameters:
'               rst:  Self-referencing Recordset containing the data
'   strPointerField:  Name of field pointing to parent's primary key
'        strIDField:  Name of parent's primary key field
'      strTextField:  Name of field containing text to be displayed
'=============================================================
Sub AddBranch(rst As Recordset, strPointerField As String, _
          strIDField As String, strTextField As String, _
          Optional varReportToID As Variant)
    On Error GoTo errAddBranch
    Dim nodCurrent As Node, objTree As TreeView
    Dim strCriteria As String, strText As String, strKey As String
    Dim nodParent As Node, bk As String
    Set objTree = Me!xTree.Object
    If IsMissing(varReportToID) Then  ' Root Branch.
        strCriteria = strPointerField & " Is Null"
    Else  ' Search for records pointing to parent.
        strCriteria = BuildCriteria(strPointerField, _
            rst.Fields(strPointerField).Type, "=" & varReportToID)
        Set nodParent = objTree.Nodes("a" & varReportToID)
    End If

    ' Find the first emp to report to the boss node.
    rst.FindFirst strCriteria
    Do Until rst.NoMatch
        ' Create a string with LastName.
        strText = rst(strTextField)
        strKey = "a" & rst(strIDField)
        If Not IsMissing(varReportToID) Then  'add new node to the parent
            Set nodCurrent = objTree.Nodes.Add(nodParent, tvwChild, strKey, strText)
        Else    ' Add new node to the root.
            Set nodCurrent = objTree.Nodes.Add(, , strKey, strText)
        End If
        ' Save your place in the recordset so we can pass by ref for speed.
        bk = rst.Bookmark
        ' Add employees who report to this node.
        AddBranch rst, strPointerField, strIDField, strTextField, rst(strIDField)
        rst.Bookmark = bk     ' Return to last place and continue search.
        rst.FindNext strCriteria   ' Find next employee.
    Loop

'--------------------------Error Trapping --------------------------
    errAddBranch:
        MsgBox "Can't add child:  " & Err.Description, vbCritical, "AddBranch Error:"
        Resume exitAddBranch
End Sub