Try sample project here -
https://mindfusion.eu/Forum/YaBB.pl?num=1493301652/3#3

but remove container handling from OnNodeRealized handler; it should now be built into the diagram.

Regards,
Slavcho
Mindfusion

Layouts do not apply recursively to containers at this time. With non-virtualizing diagram, you could call ContainerNode.Arrange(layout) for each container to arrange its child nodes, and then diagram.Arrange() to arrange the overall diagram (top-level containers). Unfortunately we do not have equivalent to ContainerNode.Arrange for VirtualizingDiaram at this time. Maybe try fully realizing all items using RealizeItems(large rect) method, arranging the containers and diagram as outlined above, and copying back the coordinates from realized diagram items to data items. You could possibly realize and arrange an offscreen VirtualizingDiagram with same data source to avoid creating all the UIElements in main diagram.

Regards,
Slavcho
Mindfusion

Try this, also check ControlPoints handling in zipped project (VirtualizingDiagram only creates single-segment links at this time):

void ArrangeContainers()
{
	var virtualDiagram = new VirtualizingDiagram();
	virtualDiagram.InstantiateNode =
		(dataItem) => InstantiateNode(virtualDiagram, dataItem);
	virtualDiagram.NodesSource = nodes;
	virtualDiagram.LinksSource = links;

	// this creates actual nodes and links for all data items
	var inifiniteViewport = new Rect(0, 0, 1000000, 1000000);
	virtualDiagram.RealizeItems(inifiniteViewport);

	// container.Arrange does not work for VirtualizingDiagram
	var offscreenDiagram = new Diagram();
	virtualDiagram.CopyTo(offscreenDiagram);

	// apply layout to containers
	var containers = offscreenDiagram.Nodes.OfType<ContainerNode>();
	foreach (var ctr in containers)
		ctr.Arrange(new TreeLayout { LinkStyle = TreeLayoutLinkType.Cascading3 });

	// apply layout to diagram
	offscreenDiagram.Arrange(
		new LayeredLayout { MultipleGraphsPlacement = MultipleGraphsPlacement.Horizontal });

	// now actual items have coordinates
	for (int i = 0; i < offscreenDiagram.Nodes.Count; i++)
	{
		var arrangedNode = offscreenDiagram.Nodes[i];
		var rect = arrangedNode.Bounds;

		var virtualNode = virtualDiagram.Nodes[i];
		var nodeData = (NodeData)virtualNode.DataContext;
		nodeData.X = rect.X;
		nodeData.Y = rect.Y;
		nodeData.Width = rect.Width;
		nodeData.Height = rect.Height;
	}
	for (int i = 0; i < offscreenDiagram.Links.Count; i++)
	{
		var arrangedLink = offscreenDiagram.Links[i];
		var points = arrangedLink.Bounds;

		var virtualLink = virtualDiagram.Links[i];
		var linkData = (LinkData)virtualLink.DataContext;
		linkData.ControlPoints = arrangedLink.ControlPoints;
	}
} 

https://mindfusion.eu/_samples/VirtualDiagLayout.zip

Regards,
Slavcho
Mindfusion