I have a fairly well-used and oft-subclassed class which overrides valueForKey:
and setValue:ForKey: to behave like the NSDictionary versions, because this
class looks much like an NSDictionary. I have a subclass of that which wants to
do 'normal' KVO, and so I need valueForKey: and setValueForKey: to return to
the default NSObject version.
I could use composition but that's a lot of boilerplate to re-expose the
properties of the composed class and I really did want it to be a subclass. I
could code up a custom valueForKey: which does the right thing, but that's
fragile if I add more properties or subclass again. So I want to actually make
the implementation of those two methods in my subclass use the NSObject
implementation.
I've messed about with +resolveClassMethod, -methodForSelector and
+instanceMethodForSelector, but found no fruit there, none of them called for
valueForKey:, so currently I have this implementation
-(id)getValueForKey:(NSString*)key
{
static IMP valueForKeyImplementation = NULL;
if( !valueForKeyImplementation )
valueForKeyImplementation = [ NSObject
instanceMethodForSelector:@selector( valueForKey: ) ];
return valueForKeyImplementation( self, _cmd, key );
}
which has a faint code odour about it. I'd prefer to find a hook where the
runtime asks me 'hello, do you have a custom IMP for this method valueForKey:'
and I can say 'yes I do and here it is', having stolen it from NSObject in the
same way. That just feels like a more collaborative way of doing it. Is there
one?
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