Hi Alastair,
I'm not sure I fully understand it either - undo issues often make my
head spin...
I *think* what's happening is that NSUndoManager is unhappy that -
removeAllActionsWithTarget: is being called while it is in the process
of discarding an invocation off its own stack. Indeed dealloc is only
getting called once but the NSUndoManager is being re-entered and
that's what it seems to be griping about. If there are no actions with
that target I guess you might get away with it, but it's quite likely
that there are (and targets are weak refs so they can still be there
even when the object is being dealloced), so maybe NSUndoManager is
trying to remove items from its stack while it is already iterating
over it discarding the invocations that are dropping out.
It's perhaps analogous to the situation of removing objects from an
array while iterating over it (but then again, who knows, the internal
workings of NSUndoManager are off-limits).
However you might be right about the ref counting bug, so I'll try and
re-examine it from that angle.
G.
On 9 Apr 2008, at 11:09 pm, Alastair Houghton wrote:
On 9 Apr 2008, at 12:23, Graham Cox wrote:
The docs for NSUndoManager state for -removeAllActionsWithTarget:
that:
"An object that shares an NSUndoManager with other clients should
invoke this message in its implementation of dealloc".
There is a problem with this - if the object being dealloced is
itself the parameter to an undo invocation, which in anything more
complicated than a trivial test case it is likely to be, then Cocoa
goes into an infinite loop when it starts discarding these
invocations off the bottom of the stack. The undo manager releases
the invocation which releases the object, which calls -
removeAllActionsWithTarget:self, and boom - it all falls over.
I'm not sure I see why you're getting into an infinite loop here. -
dealloc should be being called at most once, right?
And it shouldn't be possible to get into a situation where your
object is the parameter of an undo operation if you're already in
that object's -dealloc routine. If that's what you're seeing, you
have a reference counting bug I think.
Perhaps I'm misunderstanding the problem though?
Kind regards,
Alastair.
--
http://alastairs-place.net
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