主题：目录树增加节点或子节点时是怎样判断节点已经存在？

 遍历，看看是否有同名的。

 Dim tr As WinForm.TreeView = e.Form.Controls("TreeView1")
Dim nd As WinForm.TreeNode = tr.SelectedNode
If nd IsNot Nothing Then
    for each sn as WinForm.TreeNode in nd.nodes
        if sn.name = "abc" then
            return
        end if
    next
End If
nd.nodes.add("abc","abc")