Question

My NSArray holds two different types of classes, both of which derive from NSObject and have a method with the same name. If I call:

[myArrayList 
      makeObjectsPerformSelector:@selector(dehydrate) 
      withObject:myParamObjec];

I get the ‘unrecognized selector’ exception:

uncaught exception
‘NSInvalidArgumentException’, reason:
‘*** -[BlankItem dehydrate]:
unrecognized selector sent to instance
0x10328e0’

If I iterate through each element of ‘myArrayList’ and manually invoke ‘hydrate’ on BlankItem as a selector, same thing but if I cast correctly, everything is okay.

for (id item in myArray)
{
    if ([item isKindOfClass:[BlankItem class]])
    {
        BlankItem *blankItem = (BlankItem *)item;

        // this works
        [blankItem dehydrate:connectionFactory];

        // this produces the exception
        [item performSelector:@selector(dehydrate) withObject:myParamObjec];
    }
    else
    {
        [item performSelector:@selector(dehydrate) withObject:myParamObjec];
    }
}

Class declarations:

@interface BlankItem : NSObject {   
}

- (void)hydrate:(MyParamClass *)paramClass;
@end


@interface RegularItem : NSObject { 
}

- (void)hydrate:(MyParamClass *)paramClass;
@end

Do the two classes, BlankItem and RegularItem need to inherit from a common BaseClass in order for this to be correct?

I don’t see what I’m doing or not doing that’s producing this error. Any suggestions?

Answer 1

The selector you want is dehydrate: — you’re leaving off the colon, which makes it a completely different, colon-less selector. As far as Objective-C is concerned, the selectors “dehydrate” and “dehydrate:” are as different as “kill” and “skill”.