The overriden OnLinkSelecting

The links is removed succesfuly - it is not contained in diagram.Items anymore also not visible on view.

It looks like something is still keeping a diagram link in memory and looking at the cotract of this MRT I think its related with selection.

We are removing it from the diagram by a command that is bounded to our viewmodel. In result after few additional cleanups on our site we are calling simply Links.Remove(link).

We dont override the OnRemove. But we are subscribed to this event so I know it was called at least once after deleting the link.

Dear Slavcho,

I was able to avoid the exception.
I override the HitTest on our LinkView class

(LinkView : DiagramLink)

      public override DiagramItem HitTest(Point point, double threshold, bool onlyNodes, bool onlyInteractive, bool includeHandles, bool includeLabels)
      {
         var what = base.HitTest(point, threshold, onlyNodes, onlyInteractive, includeHandles, includeLabels);
         if (what?.Parent == null)
         {
            return null;
         }

         return what;
      }

So..

The Parent (diagram) was null for the link that was somehow kept in the memory.

The diagram that we are using shows that Items collection does not contain this link. Same as Links collection.

So it was kept somewhere in memory so the HitTest was returning it when hovering on the diagram over its previous route.

Maybe it will helps you
Cheers

For the main diagram view class we are setting the EnableSpatialIndex flag to true.

And yes we are using the ContainerNode but we are not attaching the child to its collection. We are handling this functionality by our own and the information is stored in the viewmodels.

I couldnt find the link neither in Selection nor in Active item property.

What is the source collection for this HitTest?

From a code point of view I'd say it should only lookup through the Diagram.Items/Links collection...

I managed to fix so its not so urgent..

Dear Slavcho,

as long as my fix works I will not go deeper in the investigation. If you dont see any weak spots we can put it on hold right now.
Updating the test project would be really complex when keeping in mind the complexity of our solution