Re: Using static NSString as observation context

FROM : Christiaan Hofman
DATE : Sun May 18 22:27:07 2008

On 18 May 2008, at 8:31 PM, Shawn Erickson wrote:

> On Sat, May 17, 2008 at 6:59 AM, Christiaan Hofman 
> <<email_removed>> wrote:

>> I have recently changed some KVO observation code to us a static 
>> NSString as
>> the context when registering as KVO observation. However now that 
>> seems to
>> have introduced a crasher when removing the observer, at least on a 
>> Core Duo
>> Intel machine. PPC does not seem to have any problem. So is there 
>> some
>> problem using NSStrings as observation context for Intel? The 
>> Sketch sample
>> code also uses those.

>
> Can you be more specific about the crash you are seeing? (backtrace, 
> etc.)
>


This is the top part of the crash

Thread 0 Crashed:
0 libobjc.A.dylib 0x90a59380 objc_msgSend + 16
1 com.apple.Foundation 0x928a26a7
-[NSObject(NSKeyValueObserverRegistration) removeObserver:forKeyPath:] +
233
2 com.apple.AppKit 0x93534a02 -[NSController
removeObserver:forKeyPath:] + 208

After that comes some app specific trace that clearly points to a 
particular -removeObserver:forKeyPath: on NSUserDefaultsController in -
windowWillClose: for the main document window.

> Are you removing the observation of the same key more then once? I
> have seen a over release bug in the Cocoa framework in situations like
> this (trying to locate my information on that issue...).
>
> -Shawn


No, -windowWillClose: can never be called twice, because the document 
is closed after that. And the corresponding -addObserver:... is called 
in -windowControllerDidLoadNib:, which is called for sure.

Christiaan