主题：[求助]多选目录树勾选状态

我在多选目录树下设置一个textbox，用来显示多选目录树被勾选的节点（2级节点）名称。遇到一个问题，当把勾选的节点逐个清除时，直至清空，textbox显示的节点名称仍显示最后一个被清除的节点，没能清空，是哪里原因？

Dim s As String
Dim trv As WinForm.TreeView = e.Form.Controls("TreeView1")
For Each nd As WinForm.TreeNode In trv.AllNodes
    If nd.Checked AndAlso nd.level = 1 Then
        s = s & "," & nd.Text
        If nd IsNot Nothing Then
            e.Form.Controls("TextBox3").Value = s.trim(",")
        Else
            e.Form.Controls("TextBox3").Value =""
        End If
    End If
Next