On Nov 18, 2009, at 12:00 , Corbin Dunn wrote:
On Nov 17, 2009, at 1:04 PM, Aaron Clarke wrote:
We have an application that runs fine on leopard (10.5) but
occasionally
crashes on snow leopard (10.6) when closing an NSWindow. Here is the
backtrace for the crash:
Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_PROTECTION_FAILURE at address: 0x00000000
0x976e691b in objc_msgSend ()
(gdb) bt
#0 0x976e691b in objc_msgSend ()
#1 0x197142d0 in ?? ()
#2 0x9031e88e in NSKeyValuePushPendingNotificationPerThread ()
#3 0x9031e224 in NSKeyValueWillChange ()
#4 0x9030350b in -[NSObject(NSKeyValueObserverNotification)
willChangeValueForKey:] ()
#5 0x90327cfe in _NSSetObjectValueAndNotify ()
#6 0x92745fb8 in -[NSWindow makeFirstResponder:] ()
...
Even if it doesn't crash, closing the NSWindow always results in the
following error message.
An instance 0x11b75230 of class MyWindow was deallocated while key
value
observers were still registered with it. Observation info was
leaked, and
may even become mistakenly attached to some other object. Set a
breakpoint
on NSKVODeallocateBreak to stop here in the debugger. Here's the
current
observation info:
<NSKeyValueObservationInfo 0x19408190> (
<NSKeyValueObservance 0x194233d0: Observer: 0x463afa0, Key path:
firstResponder, Options: <New: YES, Old: NO, Prior: NO> Context: 0x0,
Property: 0x4453e60>
<NSKeyValueObservance 0x1ab6ad40: Observer: 0x19427a80, Key path:
firstResponder, Options: <New: YES, Old: NO, Prior: NO> Context: 0x0,
Property: 0x4453e60>
)
I looked at what the observer object's class is, and it's a
subclass of
NSCollectionView. We do not explicitly setup a KVO relationship for
firstResponder. I also noticed that the "Application Kit Release
Notes for
Snow Leopard" mention that firstResponder is KVO-compliant, which
makes me
believe this is something new in Snow Leopard. All this
information makes
me believe this is potentially a bug in Application Kit for 10.6.
Maybe we
setup an NSCollectionView incorrectly or I'm misinterpreting this
information?
Oh -- another thing. Does your subclass of NSCollectionView override:
(void)viewWillMoveToWindow:(NSWindow *)window {
but not call super? If not... call super! Your classes should always
call super if it is defined in a superclass, unless you have a good
reason to hide the super's behavior.
corbin
This was the problem, thank you. This is a difficult bug to find in
code someone else wrote. This makes me almost wish there was a gcc
flag for it (-Woverride-no-super).
-Aaron
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