overriding a method with NSObject's version
overriding a method with NSObject's version
- Subject: overriding a method with NSObject's version
- From: Roland King <email@hidden>
- Date: Sat, 24 Nov 2012 17:55:35 +0800
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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