On Jul 30, 2005, at 11:33 AM, mmalcolm crawford wrote:
- (void)didChangeValueForKey:(NSString *)key {
if ( [key isEqualToString:@"foo"] ) {
[self setBar:[self foo] * 2]; // this change is not
reflected in the interface???
NSLog(@"%f", [self bar]);
}
}
@end
AFAIK, the object above is KVO complaint. I have an interface
with two text fields, one bound to foo and the other bound to
bar. When I change the value in the text field bound to foo the
value in the text field bound to bar doesn't change.
The accessor methods are KVO compliant, but you disrupt the
mechanism by overriding didChangeValueForKey: (specifically, you
don't invoke the superclass's implementation
I knew it was something simple, it works if I invoke the superclass'
implementation.
-- although you shouldn't be doing this anyway: is there anywhere
in the documentation that suggests that overriding the KVO
notification methods is a common pattern?).
No, there isn't.
It's not clear why you would do this rather than simply:
Well, the way I though of it was setFoo: does just that, sets foo,
and shouldn't do anything else. I thought didChangeValueForKey:
would work like a delegate method. There wasn't anything in the
documentation to make me think that, but there wasn't anything to
make me think it was the wrong thing to do either. Though, in
hindsight it was a silly thing to do.
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