Dynamically validating undo menu item availability (NSUndoManager)

FROM : Lachlan Cotter
DATE : Fri Jan 11 23:22:09 2008

Hi Cocoabuilders,


I've got a situation where I'm performing operations on the file 
system and I want those operations to be undoable. The tricky part is 
that because the file system can be changed by anyone at anytime, I 
can't necessarily assume that it will be in a state which is 
consistent with how I made my change. I have routines which can check 
for this and determine whether or not I am able to undo, but I don't 
know the best way to work with the UndoManager on this.

How can I proactively get my validation routine called and disable to 
undo menu item when it is not available?


Cheers,
Lach