[vtkusers] Adding event observer to a vtkRenderWindowInteractor changing application behavior?

[Mark Waligora]

Hey all,
I'm having a problem with setting up an event handler.  I create a class
called UpdateCallback which inherits from vtkCommand.  I override the
Execute function from vtkCommand.  My Execute function simply contains a
print statement for the time being.

In my main function, I create an instance of my class and add it as an
observer to my vtkRenderWindowInteractor for the "AnyEvent" event.

UpdateCallback* onUpdate = UpdateCallback::New();
iren->AddObserver(vtkCommand::AnyEvent, onUpdate);

When I do this, my program prints the statement in my Execute function 3
times, and then exits.  If I comment out the line of code that adds my
UpdateCallback as an observer:

// iren->AddObserver(vtkCommand::AnyEvent, onUpdate);

then the program runs as normal until you close it.  I've searched the
mailing list, googled the problem, and I've read through the code in
vtkCommand and vtkObject trying to see if adding an observer somehow changes
the behavior of the event handling.  From what I can tell, any observer
class should get called on the appropriate event, so adding my observer
shouldn't create any additional side effects besides what the code in my
observer does.  Can anyone tell me what might be going on?

Thanks a bunch in advance everyone!

-Mark
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