MVC: How best avoid nested invocations of -reloadData?

FROM : Jerry Krinock
DATE : Mon Jun 09 20:46:55 2008

My data objects are viewed in an NSOutlineView, and additional 
attributes of the selected item appear in an Inspector panel.

I have tried to implement MVC by funneling any data-model property 
change in any view to send a -changeObjectProperty::: message which 
updates the model, registers undo and sends an -updateWindow message 
to all existing window controllers.  Since the outline is editable, my 
dataSource's implementation of 
outlineView:setObjectValue:forTableColumn:byItem: does this.  To 
update the outline, the window controller of the window containing the 
outline view sends the outline view a -reloadData in its -updateWindow 
implementation.

There is a tiny problem if the user begins editing a value in the 
outline view and then, while the field editor is still key, switches 
to the Inspector panel and edits another attribute.  Method 
changeObjectProperty::: runs for the other attribute, eventually 
sending -reloadData to the outline view.  Apparently, -reloadData 
tells the outline view to end editing, which sends 
outlineView:setObjectValue:forTableColumn:byItem: to the data source, 
which invokes changeObjectProperty::: again, which sends -updateWindow 
again, which sends -reloadData again.  Actually, it all works great, 
except I get this in the console:

    "NSOutlineView Warning: reloadData called while in the middle of 
doing a reloadData!"

Which is indeed true.  Interestingly, this does not happen if editing 
the other attribute in the Inspector panel grabs the field editor.  In 
that case, the edit in the outline view is ended and its -reloadData 
is completed before the other edit begins.  The problem only occurs if 
the other edit is done in a non-text control such as a checkbox.

I've solved the problem by adding a BOOL _isReloadingData to my window 
controller and locking it so that any attempted -nested invocation of -
reloadData is skipped.  Is there a less hacky solution?  Or have I mis-
conceived MVC somewhat?  (I now know that a notification would be more 
elegant and bug-resistant than sending a bunch of -updateWindow 
messages, but I don't think that would change this issue.)

Thanks,

Jerry Krinock