tvProperties為TreeView的名稱。

  Private Sub ExpandAll_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)

            For Each item As Object In tvProperties.Items
                Dim treeItem As TreeViewItem = TryCast(tvProperties.ItemContainerGenerator.ContainerFromItem(item), TreeViewItem)
                If treeItem IsNot Nothing Then
                    ExpandAll(treeItem, True)
                End If
                treeItem.IsExpanded = True
            Next
        End Sub


      
        Private Sub ExpandAll(item As ItemsControl, expand As Boolean)
            For Each obj As Object In item.Items

                      '如果TreeViewItem未被展開過，則無法通過ItemContainerGenerator來查詢這個TreeViewItem下的子節點。

‘所以需要先將TreeViewItem的IsExpanded屬性設定為True，並呼叫UpdateLayout方法。

’即需要先展開該節點才能獲取到該節點下的子節點。也就是需要從根節點開始展開直到最末端的節點。收回時相反。

  If expand And obj IsNot Nothing And Not obj.IsExpanded Then

                    Dim tviCurrent As TreeViewItem = TryCast(item, TreeViewItem)
                    tviCurrent.SetValue(TreeViewItem.IsExpandedProperty, True)
                    tviCurrent.UpdateLayout()
                End If
                Dim childControl As ItemsControl = TryCast(item.ItemContainerGenerator.ContainerFromItem(obj), ItemsControl)
                If childControl IsNot Nothing Then
                    ExpandAll(childControl, expand)
                End If

‘閉合時則從最末端的節點往根節點收回
                If Not expand Then
                    Dim subItem As TreeViewItem = DirectCast(childControl, TreeViewItem)
                    subItem.IsExpanded=expand
                End If
            Next
        End Sub
    
        Private Sub CollapseAll_Click(ByVal sender As System.Object, ByVal e As System.Windows.RoutedEventArgs)
            For Each item As Object In tvProperties.Items
                Dim treeItem As TreeViewItem = TryCast(tvProperties.ItemContainerGenerator.ContainerFromItem(item), TreeViewItem)
                If treeItem IsNot Nothing Then
                    ExpandAll(treeItem, False)
                End If
                treeItem.IsExpanded = False
            Next


        End Sub