On Dec 23, 2008, at 04:32, Klaus Backert wrote:
The cause of the crash is the following category, I had implemented,
overriding a method of NSObject's NSKeyValueCoding category:
@interface NSObject (MyKeyValueCoding)
+ (BOOL)accessInstanceVariablesDirectly;
@end
@implementation NSObject (MyKeyValueCoding)
+ (BOOL)accessInstanceVariablesDirectly { return NO; }
@end
After having deleted this category, the application works again.
Well, there have been warnings on this mailing list about overriding
methods of Cocoa categories. I did it at my own risk. Apparently
it's too much stopping direct access of instance variables in key-
value coding for *each* and *every* class.
Well, there are actually two very major problems with the approach you
tried to use.
First, if you take away direct access to instance variables, then
*all* classes that depend on it (and there are lots of them) will
break. Randomly "deleting" functionality of existing classes is sure
to be a bad idea. (If you want to disable the functionality in all
*your* classes, the correct way would be to subclass NSObject, and
then derive all your classes from this NSObject subclass.)
Second, many methods defined on NSObject (in particular, most KVC/KVO
methods) are defined as categories. You can't reliably replace a
method in one category by redefining the method in another category,
because the order in which the categories are applied to their class
is undefined. (Again, subclassing is the way to go, if you want to
override a method that might be defined in a category.)
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