NullReference-Exception using SmartScrolling

Hi Jason,

I found another which seems to be connected to the smart scrolling of the diagram. Here is the exception:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Mindscape.WpfDiagramming.Foundation.ConnectionPointThumb.#k.#n.#o2()
   at Mindscape.WpfDiagramming.DiagramSurface.#01(Object sender, EventArgs e)
   at System.Windows.Threading.DispatcherTimer.FireTick(Object unused)
   at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   at MS.Internal.Threading.ExceptionFilterHelper.TryCatchWhen(Object source, Delegate method, Object args, Int32 numArgs, Delegate catchHandler)

What I did was starting do drag a connection until the diagram starts to scroll. At some point the connections suddenly disappears and the Exception is thrown. I was able to reproduce the issue a couple of time especially when I moved the mouse over a connection point which was disabled for a new connection by a custom validation logic. I hope this information is enough to reproduce the issue otherwise I have to create a little sample to show you this issue.

Thanks Dan

Hello Dan

Thanks for pointing this out. This seems to occur when the node where the connection is originating is panned outside the viewport and is then somehow unselected. (You may have logic somewhere that is unselecting the node when the connection drags over an invalid connection point). When a node is outside the viewport and is not the primary selected item, it is no longer rendered which causes the node to be unloaded along with the connection point and the connection adorner - which the results in the exception.

In the next nightly build, there will be a check around the smart scrolling code to avoid the null reference exception. Also, nodes that are in progress of creating a connection, and connections that are being relocated will be marked as "unvirtualizable" so that their elements stick around during the connection creation/relocation operation.

-Jason Fauchelle

Thx Jason...

I had a look at the nightly and I wasn't able to reproduce the issue anymore. Thanks a lot for the fast fix of this issue!