why does it matter where I get the mutableArrayForKey:
why does it matter where I get the mutableArrayForKey:
- Subject: why does it matter where I get the mutableArrayForKey:
- From: Roland King <email@hidden>
- Date: Sat, 02 Aug 2008 18:21:46 +0800
Still struggling with the nuts and bolts of KVC. I understood
eventually that just observing a property (test) which was an
NSMutableArray and then mutating it with removeObjectAtIndex: isn't
KVC compliant, didn't give the observers callbacks, and implemented
the removeObjectFromTestAtIndex: method. Then I finally figured out
that I can either call that method directly, or I can get
mutableArrayValueForKey:@"test" and use the normal array operations on
that proxy as it's KVC compliant.
However I failed to make it work until I moved the getter,
mutableArrayValueForKey:@"test" *after* the line I where set up my KVO
observation. If I get this mutable array beforehand, I don't get the
notification. Why does it matter when I get the
mutableArrayValueForKey:?
As the code is set up below, I won't get a KVO callback for [ test2
removeObjectAtIndex:0 ], if however you comment out the 'place one'
line and uncomment the 'place two' line, you will get the callback. In
both cases [ test2 removeObjectAtIndex:0 ] does call the
removeObjectFromTestAtIndex: method, so I would expect notificiation.
Bar *bar = [ [ Bar alloc ] init ]; // bar has one property, test, an
NSMutableArray and it has the KVC mutator methods defined.
Baz *baz = [ [ Baz alloc ] init ]; // baz has nothing but a logging
observeValueForKeyPath: method
NSMutableArray *test2 = [ bar mutableArrayValueForKey:@"test" ]; //
place one
[ bar addObserver:baz forKeyPath:@"test" options:0 context:nil ];
//NSMutableArray *test2 = [ bar
mutableArrayValueForKey:@"test" ]; // place two
// only get a callback on this one if I get the
mutableArrayValueForKey: in place two, after I've added the observer.
[ test2 removeObjectAtIndex:0 ];
// always get a KVO callback for this one
[ bar removeObjectFromTestAtIndex:0 ];
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