主题：目录树加载速度很慢是什么原因？

下面这段代码，在双击的时候，结果没有出错，但是在加载的速度上很慢，我数据库只有300条数据，但是筛选后加载的时间需要3-4秒钟，并切目录树会有2秒钟的空白，然后再恢复显示。问题是出在什么地方呢？ 谢谢！

Dim Filter As String

Dim dr As DataRow = e.Node.DataRow '获取生成此节点的行

If e.Node.Text <> "显示所有数据......" Then

    Dim Year As Integer = e.Node.DataRow("年")

    Dim Month As Integer = e.Node.DataRow("月")

    Dim gb As String = e.Node.DataRow("车别")

    Dim khdm As String = e.Node.DataRow("客户代码")

    Select Case e.Node.Level

        Case 0

            Filter = "1>1"

            e.Form.Controls("Button6").Visible = False

e.Form.Controls("Button02").Visible = False

            Vars("车别") = ""

        Case 1

            Filter = "1>1"

            e.Form.Controls("Button6").Visible = False

e.Form.Controls("Button02").Visible = False

            Vars("车别") = ""

        Case 2

            Filter ="Year(装车日期) = " & Year & " And Month(装车日期) = " & Month & " And 车别 = '" & gb & "'"

            e.Form.Controls("Button6").Visible = True

            e.Form.Controls("Button02").Visible = True

            Vars("车别") = gb

            Vars("筛选条件") = "车别 = '" & gb & "'"

        Case 3

            Filter ="Year(装车日期) = " & Year & " And Month(装车日期) = " & Month & " And 车别 = '" & gb & "' and 客户代码 = '" & khdm & "'"

            Vars("车别") = gb

            e.Form.Controls("Button6").Visible = True

            e.Form.Controls("Button02").Visible = False

    End Select

End If

DataTables("装车明细").loadFilter = Filter

DataTables("装车明细").Load()