Hi Marc and Quincy
On 19/3/09, m...@sky4studios.be wrote:
'NSInternalInconsistencyException', reason: 'Cannot remove an observer
<Observer 0x10ac00> for the key path "targetPhoto.name" from
<NSMyArrayController 0x1099d0>, most likely because the value for the
key "targetPhoto" has changed without an appropriate KVO notification
being sent. Check the KVO-compliance of the NSMyArrayController class.'
That is indeed a real problem and one which can take a lot of
time from you. In some cases the scenario really is what the
message above is saying. Other times, I think, its something
else, or a bug. Re the former, I had a simple app that was
getting that problem but which looked fine to me. I showed the
code to a bright young man on this mailing list named Hamish
Allen and he immediately saw the problem and suggested a fix,
which worked perfectly. (See footnote.) To this day, I can't
say I completely understand why his fix worked.
I had the same problem in a much more complex app. It was a
sort of master-slave display of models and their specific
products. If I changed the model for a product I got the
error. I discovered that the fields in the product list which
actually belonged to the model were causing the problem. For
example, in the product list, I showed the product category name
via this binding [self.]model.category.name. In the end I
hacked it to work by changing the binding to selectedmodel.category.name.
I shudder to think of the number of hours I spent trying to
ensure KVO compliance and to really understand this problem.
Your best bet might be to throw yourself at the feet of the
talented Mr Allen -- or perhaps you can gain his skills
yourself. I've pasted below an excerpt from his masterful email
-- maybe you can glean something useful from it.
Good luck,
Steve
from Hamish Allen
"Cannot remove an observer <NSTableBinder 0x166d00> for the key path
"contributionForSelectedDecisionValue.degree" from <Alternative
0x1a90a0>, most likely because the value for the key
"contributionForSelectedDecisionValue" has changed without an
appropriate KVO notification being sent. Check the
KVO-compliance of
the Alternative class."
The problem there was pretty much exactly as the error message
describes: the Contribution in question is being dynamically selected
within the method contributionForSelectedDecisionValue, and said
method is free to return a different object than the one it returned
last time it was called, without
willChangeValueForKey:@"contributionForSelectedDecisionValue" having
been called in the interim.
This is confirmed by changing the table column binding from
"contributionForSelectedDecisionValue.degree' to
'degreeForContributionForSelectedDecisionValue' and writing the
following code:
- (NSNumber *)degreeForContributionForSelectedDecisionValue
{
return [[self contributionForSelectedDecisionValue] degree];
}
+ (NSSet *)keyPathsForValuesAffectingValueForKey:(NSString *)key
{
if ([key isEqualToString:@"degreeForContributionForSelectedDecisionValue"])
return [NSSet setWithObject:@"contributionForSelectedDecisionValue"];
else
return [super keyPathsForValuesAffectingValueForKey:key];
}
No exception is thrown with this new binding.
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