请求修改VB.NET代码实现SQL Server表填充三级TreeView

以下是修改后的完整代码，实现从TrvBook表读取GrandLedgers（一级节点）、Ledgers（二级节点）、Persons（三级节点）构建三级TreeView：

Dim query As String = "SELECT GrandLedgers, Ledgers, Persons FROM TrvBook WHERE ID = @OwnerID"

Using con = New SqlConnection(ConString)
    Using cmd = New SqlCommand(query, con)
        cmd.Parameters.Add(New SqlParameter("@OwnerID", My.Settings.OwnerID))

        con.Open()

        Dim dt As SqlDataReader = cmd.ExecuteReader
        Dim currentGrandLedger As String = ""
        Dim currentLedger As String = ""
        Dim grandNode As TreeNode = Nothing
        Dim ledgerNode As TreeNode = Nothing

        While dt.Read
            Dim gl As String = dt("GrandLedgers").ToString()
            Dim l As String = dt("Ledgers").ToString()
            Dim p As String = dt("Persons").ToString()

            ' 处理一级节点：GrandLedgers
            If gl <> currentGrandLedger Then
                currentGrandLedger = gl
                grandNode = TreeViewBook.Nodes.Add(gl)
                currentLedger = "" ' 切换一级节点后重置二级节点跟踪
                ledgerNode = Nothing
            End If

            ' 处理二级节点：Ledgers
            If l <> currentLedger Then
                currentLedger = l
                ledgerNode = grandNode.Nodes.Add(l)
            End If

            ' 添加三级节点：Persons
            ledgerNode.Nodes.Add(p)
        End While
    End Using
End Using

TreeViewBook.ExpandAll()

关键改动说明 #

• 新增currentLedger和ledgerNode变量，跟踪当前二级节点状态，避免重复创建相同二级节点
• 不再依赖TreeViewBook.SelectedNode操作节点，改用变量直接引用对应层级节点，逻辑更稳定
• 依次判断一级、二级节点是否已存在，不存在则创建，最后统一添加三级节点Persons
• 使用字段名dt("GrandLedgers")替代索引dt.Item(0)，代码可读性更强

内容的提问来源于stack exchange，提问作者user24059174