Hi,

You can use the PathFinder class for this. Its FindCycle method will let you find out if a cycle already exists.

If you need to prevent users from creating cycles interactively, call PathFinder.FindShortestPath(e.Destination, e.Origin) from the LinkCreating handler, and if it finds a path set e.Cancel = true; an existing path from destination to origin means the new link would create a cycle.

I hope that helps,
Stoyan