Methods in super that will be subclassed anyway (Cocoa)

Question

Sorry if this is a repost but I couldn't quite search for it because I can't explain it in a few words. I have a super class with lots of methods but they will always (not all of them) be subclassed. From the super I need to run those methods. I could either leave the methods in super empty or I could just not type them in super but call them anyway like so [self myMethod] and it will call my subclassed method even if it doesn't exist in super. This works but Xcode gives me an error though. 'superclass' may not respond to '-subclassmethod'

What should I do so I won't get the warnings?

Answer 1

I prefer to define the unimplemented methods in the superclass like this:

@interface GLObject : NSObject {}
- (id)someSubclassProvidedMethod;
@end

@implementation GLObject
- (id)someSubclassProvidedMethod {
  [self doesNotRecognizeSelector: _cmd];
}
@end

It's almost entirely redundant, because the Objective-C runtime would eventually call -doesNotRecognizeSelector: if I didn't define the method at all. But because I do define it, it's in the class's interface which both keeps the compiler happy and provides me with some documentation.

Answer 2

I lately like using NSAssert for this task:

- (BOOL)proceedForVersion:(int)versionInteger
{
    NSAssert(false, @"This method needs to be overridden in a subclass of iMBApertureAbstractParser");

    return NO;
}

Answer 3

Rather than the superclass, you could declare the methods in a protocol, what is called a "interface" in other languages.

@protocol MyProtocol
-(id)myMethodWith:(id)arg;
@end

Change the type declaration of the variables to declare that the object conforms to the protocol.

-(id)doStuffWith:(SuperClass <MyProtocol> *)aThing and:(id)another {
    return [aThing myMethodWith:another]
}

Note that you won't be able to pass an instance of your SuperClass to doStuffWith:and:, since it won't implement MyProtocol, but it sounds like that's what you want.

Answer 4

My solution was a little weird, but here it is:

@protocol JSDog <NSObject>
- (void)yipe;
@end

@interface JSDog : NSObject
@end

@implementation JSDog

+ (void)initialize {
  if ([self isSubclassOfClass:[JSDog class]] && ![self conformsToProtocol:@protocol(JSDog)]) {
    NSAssert(false, @"Subclasses of JSDog must conform to <JSDog>.");
  }
}

@end

Having a protocol with the same name as a class is precedented in NSObject. Because methods in a formal protocol a by default @required, you will be protected on both ends: in compile-time, if your JSDog subclass purports to conform to <JSDog>, but doesn't implement -yipe, you will receive an error; at runtime, if your subclass does not claim to conform with <JSDog>, you will receive a warning when the subclass is instantiated.