□提要:在VB6中,常将TreeView用...... 提要:在VB6中,常将TreeView用来表示层次数据,但相关的与数据库进行交互的代码,需要大量的采用手工编码;在VB.Net中,由于数据绑定功能的加强及语言特性的增强,可以很容易的实现TreeView与层次数据的绑定,本文将首先建立一个继承自TreeView的 dbTreeView,然后用一个单位(部门)的层次数据与dbTreeView进行数据绑定,并提供了与数据库进行交互的代码。 1、从层次数据的表达方式开始 在本例中,部门表(department)中有五个字段,如下表: 字段名字段类型说明 ID自动编号Key CodeString编码 NameString名称 PIDInt父结点的ID CPtrboolean是否有子结点 2、继承自TreeNode的myTreeNode 在myTreeNode中,新增了三个属性,如下表: 属性名类型说明 ValueObjectKey PIDObject父结点的ID CPtrBoolean是否有子结点 在Init事件中,根据传入的四个参数,设置这三个属性和Text属性。 3、将dbTreeView绑定到数据源 属性名类型说明 DatasourcedataviewdbTreeVIew的数据源使用dataview,而不是object ValueMemberstring值成员(数据源[dataview]的列名) DisplayMemberstring显示(在Text中)成员 PidMemberstring父ID成员 CPtrMemberstring是否有子结点 后四个属性对应myTreeNode的value,text,pid,cptr。 相关代码如下: Protected Property DataSource() As Object Get Return mDataView End Get Set(ByVal Value As Object) If Value Is Nothing Then Else mDataView = Value cm = CType(Me.BindingContext(mDataView), CurrencyManager) UpdateTreeView() End If End Set End Property Protected Property PidMember() As String Get Return mPidMember End Get Set(ByVal Value As String) mPidMember = Value End Set End Property Protected Property DisplayMember() As String Get Return Join(mDisplayMember, SplitChar) End Get Set(ByVal Value As String) mDisplayMember = Split(Value, SplitChar) End Set End Property '注意,这几个属性都是保护成员,必须在Init事件中设置: Public Sub Init(ByVal dispmember As String, ByVal valuemember As String, ByVal pidmember As String, ByVal cptrmember As String, ByVal datasource As DataView) Me.ValueMember = valuemember Me.DisplayMember = dispmember Me.PidMember = pidmember Me.CPtrMember = cptrmember Me.DataSource = datasource '取value最大值,新增时将value+1,保证关健值唯一。 Me.mDataView.Sort = Me.ValueMember Me.m_MaxID = Me.GetValue(Me.mDataView.Count - 1) End Sub 设置DisplayMember属性的格式如:字段1;字段2;字段3…,在设置属性时,将传来的参数转换为字符串数组mDisplayMember,在检索值时返回数据如:值1 值2 值3.… Protected Overridable Function GetDisplay(ByVal Index As Integer) As Object Dim i As Integer Dim temp As String = "" For i = 0 To mDisplayMember.Length - 1 temp = temp & IIf(i > 0, LinkChar, "") & mDataView(Index)(mDisplayMember(i)) Next Return temp End Function 其它检索值的函数请参见源程序。 生成树 UpdateTreeView调用私有方法FillTree来生成树,需要注意的,FillTree只是生成指定结点的子结点并将其添加到指定结点,而不是一次就将所有结点添加到树中,如果未指定结点(第一次填充时),只是添加顶层结点。 Private Sub FillTree(ByRef pnode As myTreeNode, Optional ByVal filter As String = "") mDataView.RowFilter = filter Dim i As Integer, icol As Integer Dim newnode As myTreeNode RemoveHandler cm.PositionChanged, AddressOf cm_PositionChanged Me.BeginUpdate() For i = 0 To mDataView.Count() - 1 newnode = New myTreeNode(GetDisplay(i), GetValue(i), GetPid(i), GetCPtr(i)) '当有子结点时,为这个结点添加一个空子结点 If newnode.CPtr Then Dim nullnode As New myTreeNode() nullnode.Value = NoExpandNodeValue newnode.Nodes.Add(nullnode) End If If pnode Is Nothing Then Me.Nodes.Clear() Me.Nodes.Add(newnode) Else pnode.Nodes.Add(newnode) End If Next Me.EndUpdate() mDataView.RowFilter = "" AddHandler cm.PositionChanged, AddressOf cm_PositionChanged End Sub 在展开有子结点的结点前,删除所有子结点,再用FillTree为待展开结点新增子结点。 Private Sub dbTreeView_BeforeExpand(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewCancelEventArgs) Handles MyBase.BeforeExpand '当是新增结点引起BeforeExpand事件时,直接退出。 If ExpandWhenAddNode Then Exit Sub '在展开结点前更新子结点 Dim currentnode As myTreeNode = CType(e.Node, myTreeNode) With currentnode .Nodes.Clear() FillTree(currentnode, mPidMember & "= " & CInt(.Value)) End With End Sub 4、实现数据与绑定控件的同步 要实现两个方面的同步: 1、 其它绑定控件(如textbox等)应与TreeView当前结点所指向的记录位置一致。 Private Sub dbTreeView_AfterSelect(ByVal sender As Object, ByVal e As System.Windows.Forms.TreeViewEventArgs) Handles MyBase.AfterSelect If e.Node Is Nothing Then Exit Sub '定位到position cm.Position = GetPosition(CType(e.Node, myTreeNode).Value) If AllowEdit Then oldNode = e.Node oldPos = cm.Position End If End Sub 2、在其它绑定控件改变了数据源后,更新树结点,这个工作在触发CurrencyManager的PositionChanged事件时进行。 Public Sub cm_PositionChanged(ByVal sender As Object, ByVal e As System.EventArgs) If CType(Me.SelectedNode, myTreeNode).Value <> GetValue(cm.Position) Then Debug.WriteLine("Current node isn't correct point to currencymanager.position!") Me.SelectedNode = FindNodeByValue(GetValue(cm.Position), Me.Nodes) End If If AllowEdit Then If Me.SelectedNode Is Nothing AndAlso cm.Position = cm.Count - 1 Then '当新增记录时,新增树结点 If CType(cm.Current, DataRowView).IsNew Then Me.SelectedNode = AddNode(cm.Position) Exit Sub End If End If If Not oldNode Is Nothing Then If CType(oldNode, myTreeNode).Value = GetValue(oldPos) Then '更新老结点 oldNode.Text = GetDisplay(oldPos) Else End If End If End If End Sub 使用dbTreeView 程序运行后界面如下: 相关代码请参见源程序,这里不做详述,需要注意的是删除操作并没有删除子结点,只是删除当前结点而已,删除子结点的工作应该在存储过程中递归实现,而不应放在前端。 |
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