On Jun 6, 2015, at 14:35 , Cosmo <[email protected]> wrote:
>
> Can somebody explain to me why I’m getting this different behavior. Is there
> anything I can do to achieve my goal?
The most likely immediate reason is that the class returned by '[self
classToUseForBackend]’ doesn’t actually implement a method called
‘errorMessageForCode:’. If you think it does, check the spelling and
capitalization of the method name in the subclass.
However, the code fragments you show here don’t make any sense. Class methods
in Obj-C (methods with a ‘+’) have inheritance like instance methods. So, if a
subclass implements (say) ‘logout’, execution is never going to reach the
superclass implementation. If a subclass *doesn’t* implement (say)
‘errorMessageForCode:’, you’re going to get an infinite loop.
Furthermore, if the subclass method happens to call the ‘super’ method, then
you will again end up with an infinite loop.
If your intention is to have a class hierarchy where the base class defines
methods that the subclass must implement — that is, where the base class has
abstract methods — there are two straightforward ways:
1. Define the base class method but don’t do anything in it, except possibly to
cause an exception:
+ (void) logout {
NSAssert (NO, @“Subclass responsibility”);
}
2. Use a protocol instead of a base class:
@protocol BaseClassProtocol
+ (void) logout;
@end
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