Windows Forms 控制項開發：擴充 TreeView 資料繫結與 CurrencyManager 同步（四）

保持多控制項資料繫結同步

CurrencyManager 除存取繫結資料源外，尚可協調共用同一 DataSource 的多個控制項，確保停留在同一資料項。覆寫 OnAfterSelect，選取樹節點時設定 CurrencyManager.Position 為當前項索引。

自訂 TreeNode 類別 (TreeLeafNode/TreeGroupNode) 內建 Position 屬性儲存列表索引：

Protected Overrides Sub OnAfterSelect(ByVal e As TreeViewEventArgs)
    Dim tln As TreeLeafNode
    If TypeOf e.Node Is TreeGroupNode Then
        tln = FindFirstLeafNode(e.Node)
        RaiseEvent AfterGroupSelect(New GroupTreeViewEventArgs(e))
    ElseIf TypeOf e.Node Is TreeLeafNode Then
        RaiseEvent AfterLeafSelect(New LeafTreeViewEventArgs(e))
        tln = CType(e.Node, TreeLeafNode)
    End If
    If Not tln Is Nothing AndAlso cm.Position <> tln.Position Then
        cm.Position = tln.Position
    End If
    MyBase.OnAfterSelect(e)
End Sub

Private Function FindFirstLeafNode(ByVal currNode As TreeNode) As TreeLeafNode
    If TypeOf currNode Is TreeLeafNode Then Return CType(currNode, TreeLeafNode)
    If currNode.Nodes.Count > 0 Then Return FindFirstLeafNode(currNode.Nodes(0))
    Return Nothing
End Function

回應 CurrencyManager 事件同步選取項

CurrencyManager 引發三事件：PositionChanged、ItemChanged、CurrentChanged。採用 PositionChanged 變更選取節點：

Private Sub cm_PositionChanged(ByVal sender As Object, ByVal e As EventArgs) Handles cm.PositionChanged
    Dim tln As TreeLeafNode
    If TypeOf Me.SelectedNode Is TreeLeafNode Then
        tln = CType(Me.SelectedNode, TreeLeafNode)
    Else
        tln = FindFirstLeafNode(Me.SelectedNode)
    End If
    If tln.Position <> cm.Position Then
        Me.SelectedNode = FindNodeByPosition(cm.Position)
    End If
End Sub

Private Function FindNodeByPosition(ByVal index As Integer) As TreeNode
    Return FindNodeByPosition(index, Me.Nodes)
End Function

Private Function FindNodeByPosition(ByVal index As Integer, ByVal NodesToSearch As TreeNodeCollection) As TreeNode
    Dim i As Integer = 0
    Do While i < NodesToSearch.Count
        Dim currNode = NodesToSearch(i); i += 1
        If TypeOf currNode Is TreeLeafNode Then
            Dim tln = CType(currNode, TreeLeafNode)
            If tln.Position = index Then Return currNode
        Else
            Dim found = FindNodeByPosition(index, currNode.Nodes)
            If found IsNot Nothing Then Return found
        End If
    Loop
    Return Nothing
End Function

建議若資料源支援 IBindingList，可改用 ListChanged 事件。