I've found the same problem in a Core Data app where managed objects
are changed by a background thread calling back to the main thread
over several iterations of the event loop, and I need to cancel them
as a group. Here is the trick I used...
NSUndoManager* mgr = [moc undoManager];
// Undo the cancelled operation.
[mgr undo];
// Now clear this incomplete operation from the redo stack by
// putting a dummy operation on the undo stack and then removing it.
[mgr registerUndoWithTarget:dummyRetainedObject
selector:@selector(self) object:nil];
// The action must be removed on the next iteration of the event
// loop in order to make sure the undo group is closed.
[mgr performSelector:@selector(removeAllActionsWithTarget:)
withObject:dummyRetainedObject afterDelay:0.];
On Jul 12, 2009, at 11:05 AM, Greg Titus wrote:
On Jul 12, 2009, at 7:10 AM, John Nairn wrote:
I added an option to cancel some action in the middle of the
action. The most convenient coding was to implement the cancel by
calling undo in the NSUndoManager, but this adds a "Redo" action to
redo the partial or incomplete changes (and leaves the data in a
poor state).
I can either re-code the change process or for an alternative, is
there a way to perform to top level undo without having it moved to
the redo stack? Or, similarly, is there a way to perform an undo
and then remove the top most item in the redo stack?
First, I'd agree with I.S. that this sounds a little bit unclean,
and that if there is a way to rearchitect this, I would.
Can't think of a cleaner way that wouldn't require and awful lot of
caching changes before applying them. This would require a lot more
code and potential for bugs when the undo mechanism does it perfectly.
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