Re: [Pyobjc-dev] the mysterious attribute error

[Ronald O. <ous...@ci...>]

On 28-mrt-04, at 4:11, Burris T. Ewell wrote:

> Okay, I've removed all of the threads from my application.  It's  
> completely kosher.  I use NSTasks for the workers, and DO for  
> callbacks.  It works just fine most of the time.  When I click around  
> between rows, especially when one or more rows are getting frequent  
> updates, I get the weird crash with the disappearing attribute when  
> the cell is redrawing.  A race condition that causes objects to get  
> decref'd?

 From Subclassing NSCell at  
http://developer.apple.com/documentation/Cocoa/Conceptual/ControlCell/ 
index.html#//apple_ref/doc/uid/10000015i:

<quote>
If the subclass contains instance variables that hold pointers to  
objects, consider overriding copyWithZone: to duplicate the objects.  
The default version copies only pointers to the objects.
</quote>

You should implemented copyWithZone: unless you subclass has '__slots__  
= ()', otherwise the copy of a cell will share its __dict__ with the  
original, without updating the reference count. That will give problems  
later on.

Ronald
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