詳解ASP.NET樹形圖
ASP.NET樹形圖用于顯示按照樹形結構進行組織的數據，其用途比較廣泛，如計算機中的文件系統(Windows中的資源管理器)、企業或公司的組成結構等。我們知道在Windows下VB、PB、Delphi等工具提供了一個功能很強的樹型控件TreeView，利用Treeview控件可以方便地開發樹形圖。然而在網頁上實現樹形圖就不那么容易了，現在在ASP.NET中利用微軟提供的Internet Explorer WebControls它使得網頁上的樹形圖開發與在Windows下一樣的方便，一樣的功能強大，甚至更靈活。
本文介紹用Internet Explorer WebControls開發ASP.NET樹形圖的方法，由于樹形圖結構較復雜，使用起來常不知如何下手。筆者結合最近剛為公司用ASP.NET編寫的應用程序管理器這一具體實例，詳細闡述在ASP.NET下如何將Internet Explorer WebControls的使用與數據庫聯系起來，實現數據分任意多層顯示，方便地進行增加、修改、刪除、移動操作。筆者希望通過對該實例的闡述，達到拋磚引玉的效果，與各位同仁相互交流，共同進步。
一、樹的建立
具體方法是：創建一個數據庫，設計樹圖信息表TREE_INFO，包含NODEID、PARENTID、NODENAME、ADDERSS、ICON字段，其它字段根據實際業務而定，節點名稱NODENAME將在樹型控件的節點上顯示，NODEID字段保存節點的***標識號，PARENTID表示當前節點的父節點號，標識號組成了一個“鏈表”，記錄了樹上節點的結構。設計一個Web窗體其上放置TreeView控件。
- Private Sub CreateDataSet()’建立數據集
- Dim myConn As New SqlConnection()
- Dim myCmd As New SqlCommand("select NODEID,NODENAME,PARENTID,
ADDRESS,ICON from Tree_info", myConn)- Dim myDataAdapter As New SqlDataAdapter()
- myConn.ConnectionString = Application("connectstring")
- myCmd.CommandText = ""
- myCmd.Connection = myConn
- myDataAdapter.SelectCommand = myCmd
- myDataAdapter.Fill(ds, "tree")
- End Sub
建樹的基本思路是：從根節點開始遞歸調用顯示子樹
- 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、刪除樹節點
單純在Treeview 上增加、刪除、修改節點只需用Nodes屬性的Add、 Remove、等方法即可，值得注意的地方是VS.NET中Treeview的Nodes集合與VS6.0中的區別，VS6.0中的是一個大的集合，而 VS.NET中的是分層的每個Node下都有Nodes屬性。增加、刪除、修改樹節點時與VS6.0相比有很大差別，特別是刪除時。
Private Sub ButAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButAdd.Click’在選定的節點下添加子節點
- Dim tmpNd As New TreeNode(), NdSel As TreeNode
- tmpNd.ID = GetNewId()
- NdSel = TreeView1.GetNodeFromIndex(TreeView1.SelectedNodeIndex)’選中的節點
- tmpNd.Text = "新節點"
- NdSel.Nodes.Add(tmpNd)
- Dim myRow As DataRow
- myRow = ds.Tables("tree").NewRow()
- myRow("NODE_NAME") = tmpNd.ID
- myRow("NODE_DESCRIPT") = "新節點" & 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’刪除選中的節點- 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
- ‘獲得選中節點的父節點的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
- tmpNdstmpNds = tmpNds(CInt(idxs(i))).Nodes
- Next
- End If
- Return tmpNds
- End Function
三、修改、移動樹節點
由于服務器控件不支持鼠標拖動事件，所以不能象Windows程序那樣通過拖動移動節點，這里是通過選擇父節點的方式。移動是通過在原位置刪除，新位置添加實現的，要注意在刪除時先保存節點信息。
- 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
- ‘移動節點
- 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’新的父節點的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- ‘由關鍵字查找節點
- 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
四、結束語
以上闡述ASP.NET樹形圖，以及如何在對樹節點進行維護（增加、刪除、修改、移動）的同時，修改數據庫數據。由于篇幅所限，筆者在此只對基本思路和流程及關鍵步驟作了介紹，并未列出詳細源代碼，讀者可自行完善。需要詳細源代碼者可與我聯系，本文程序在VS.NET、SQLServer、 Windows 2000、IIS5.0下調試通過。
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