树形图用于显示按照树形结构进行组织的数据，其用途比较广泛，如计算机中的文件系统(Windows中的资源管理器)、企业或公司的组成结构等。我们知道在Windows下VB、PB、Delphi等工具提供了一个功能很强的树型控件TreeView，利用Treeview控件可以方便地开发树形图。然而在网页上实现树形图就不那么容易了，现在在ASP.NET中利用微软提供的Internet Explorer WebControls它使得网页上的树形图开发与在Windows下一样的方便，一样的功能强大，甚至更灵活。

　　本文介绍用Internet Explorer WebControls开发树形图的方法，由于树形图结构较复杂，使用起来常不知如何下手。笔者结合最近刚为公司用ASP.NET编写的应用程序管理器这一具体实例，详细阐述在ASP.NET下如何将Internet Explorer WebControls的使用与数据库联系起来，实现数据分任意多层显示，方便地进行增加、修改、删除、移动操作。笔者希望通过对该实例的阐述，达到抛砖引玉的效果，与各位同仁相互交流，共同进步。

　　Internet Explorer WebControls不在VS.NET的标准Server Control中，要到微软的站点上下载，下载地址是：http://msdn.microsoft.com/downloads/samples/internet/default.asp?url=/Downloads/samples/Internet/ASP_DOT_NET_ServerControls/WebControls/default.asp 下载安装后第一次使用时，要右击工具箱Customize Toolbox…→.NET Framework Components中找到Micosoft.Web.UI.WebControls.Treeview后选中，这样Treeview控件就出现在工具箱中了。

　　一、树的建立

　　具体方法是：创建一个数据库，设计树图信息表TREE_INFO，包含NODEID、PARENTID、NODENAME、ADDERSS、ICON字段，其它字段根据实际业务而定，节点名称NODENAME将在树型控件的节点上显示，NODEID字段保存节点的唯一标识号，PARENTID表示当前节点的父节点号，标识号组成了一个“链表”，记录了树上节点的结构。设计一个Web窗体其上放置TreeView控件。

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load 
CreateDataSet() 
intiTree(TreeView1.Nodes, 0) 
End Sub 
Private Sub intiTree(ByRef Nds As TreeNodeCollection, ByVal parentId As Integer) 
Dim dv As New DataView() 
Dim drv As DataRowView 
Dim tmpNd As TreeNode 
Dim intId As Integer 
dv.Table = ds.Tables("tree") 
dv.RowFilter = "PARENTID=’" & parentId & "’" 
For Each drv In dv 
tmpNd = New TreeNode() 
strId = drv("NODE_ID") 
tmpNd.ID = strId 
tmpNd.Text = drv("NODE_NAME ") 
tmpNd.ImageUrl = drv("ICON").ToString 
Nds.Add(tmpNd) 
intiTree(Nds(Nds.Count - 1).Nodes, intId) 
Next 
End Sub 

二、增加、删除树节点 　　单纯在Treeview 上增加、删除、修改节点只需用Nodes属性的Add、 Remove、等方法即可，值得注意的地方是VS.NET中Treeview的Nodes集合与VS6.0中的区别，VS6.0中的是一个大的集合，而VS.NET中的是分层的每个Node下都有Nodes属性。增加、删除、修改树节点时与VS6.0相比有很大差别，特别是删除时。

Private Sub ButAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButAdd.Click’在选定的节点下添加子节点 
Dim tmpNd As New TreeNode(), NdSel As TreeNode 
tmpNd.ID = GetNewId() 
NdSel = TreeView1.GetNodeFromIndex(TreeView1.SelectedNodeIndex)’选中的节点 
tmpNd.Text = "新节点" 
NdSel.Nodes.Add(tmpNd) 
Dim myRow As DataRow 
myRow = ds.Tables("tree").NewRow() 
myRow("NODE_NAME") = tmpNd.ID 
myRow("NODE_DESCRIPT") = "新节点" & tmpNd.ID & "_" & NdSel.ID 
myRow("PARENT_NAME") = NdSel.ID 
ds.Tables("tree").Rows.Add(myRow) 
End Sub 
Private Sub ButDele_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles ButDele.Click’删除选中的节点 
Dim idx As String = TreeView1.SelectedNodeIndex() 
GetNdCol(idx).Remove(TreeView1.GetNodeFromIndex(idx)) 
Dim dv As New DataView(), recNo As Integer 
dv.Table = ds.Tables("tree") 
dv.RowFilter= "NODEID=" & NdId 
dv.Delete(0) 
End Sub 
Private Function GetNdCol(ByVal idx As String) As TreeNodeCollection 
‘获得选中节点的父节点的Nodes集合 
Dim cnt As Integer, i As Integer 
Dim tmpNds As TreeNodeCollection 
Dim idxs() As String 
idxs = Split(idx, ".") 
cnt = UBound(idxs) 
If cnt = 0 Then 
tmpNds = TreeView1.Nodes 
Else 
tmpNds = TreeView1.Nodes(CInt(idxs(0))).Nodes 
For i = 1 To cnt - 1 
tmpNds = tmpNds(CInt(idxs(i))).Nodes 
Next 
End If 
Return tmpNds 
End Function

Private Sub TreeView1_SelectedIndexChange(ByVal sender As Object, ByVal e As Microsoft.Web.UI.WebControls.TreeViewSelectEventArgs) Handles TreeView1.SelectedIndexChange 
Dim dv As New DataView() 
dv.Table = ds.Tables("tree") 
Dim tmpNd As TreeNode = TreeNdSel(e.OldNode), tmpNds As TreeNodeCollection 
dv.RowFilter= "NODEID=" & tmpNd.ID 
dv(0)("NODE_DESCRIPT") = Me.TextBox1.Text 
dv(0)("ADDRESS") = Me.TextBox2.Text 
dv(0)("TARGET") = Me.TextBox3.Text 
dv(0)("ICON") = Me.TextBox4.Text 
If dv(0)("PARENTID").ToString <> Me.DropDownList1.SelectedItem.Value Then 
‘移动节点 
dv(0)("PARENT_NAME") = Me.DropDownList1.SelectedItem.Value 
If Me.DropDownList1.SelectedItem.Value = "ROOT" Then 
tmpNds = TreeView1.Nodes 
Else 
tmpNds = FromIdToNode(Me.DropDownList1.SelectedItem.Value, TreeView1.Nodes).Nodes’新的父节点的Nodes集合 
End If 
GetNdCol(e.OldNode).Remove(tmpNd) 
tmpNds.Add(tmpNd) 
End If 
tmpNd.Text = Me.TextBox1.Text 
tmpNd.ImageUrl = Me.TextBox4.Text 
tmpNd = TreeView1.GetNodeFromIndex(TreeView1.SelectedNodeIndex) 
dv.RowFilter= "NODEID=" & tmpNd.ID 
Me.TextBox1.Text = dv(0)("NODENAME").ToString 
Me.TextBox2.Text = dv(0)("ADDRESS").ToString 
Me.TextBox3.Text = dv(0)("TARGET").ToString 
Me.TextBox4.Text = dv(0)("ICON").ToString 
End Sub 
Private Function FromIdToNode(ByVal ID As String, ByVal Nds As TreeNodeCollection) As TreeNode 
‘由关键字查找节点 
Dim i As Integer 
Dim tmpNd As TreeNode, tmpNd1 As TreeNode 
For Each tmpNd In Nds 
If tmpNd.ID = ID Then 
Return tmpNd 
Exit Function 
End If 
tmpNd1 = FromIdToNode(ID, tmpNd.Nodes) 
If Not (tmpNd1 Is Nothing) Then 
Return tmpNd1 
Exit Function 
End If 
Next 
Return Nothing 
End Function