如何将派生类方法委托给协议方法？

Question

I am very new to Objective C. Please excuse me if you find my question very naive. I tried searching on web, but due to lack of good context, search results don't seem to fit my requirement.

I have a method foo declared in protocol P . interface Derived inherit from P and provide implementation of foo . I have another interface AnotherDerived which inherit from protocol P . I want to delegate call from method of AnotherDerived to foo so that Derived method gets invoked.

@protocol P <NSObject>
@required

- (NSString *)foo;

@end

@interface Derived: NSObject <P>
- (NSString *)foo
{
    return _foo;
}
@end

@interface AnotherDerived: NSObject <P>
- (NSString *)foo
{
    return [super foo];  <----------------- I need something like this. It should call method of Derived
}
@end

Is there a way to do this?

Answer 1

Simply because two classes implement the same protocol, doesn't mean that there is some relationship between those two classes. The foo method in AnotherDerived has no knowledge that there is some other class, Derived , that also implements foo .

You could allocate an instance of Derived explicitly in AnotherDerived 's foo and use that:

@interface AnotherDerived: NSObject <P>
- (NSString *)foo
{
    Derived *d = [Derived new];
    return [d foo];
}
@end

Or you could potentially declare foo as a class method:

@protocol P <NSObject>
@required

+ (NSString *)foo;

@end

@interface Derived: NSObject <P>
+ (NSString *)foo
{
    return _foo;
}
@end

But you would still need to explicitly invoke foo from Derived

@interface AnotherDerived: NSObject <P>
+ (NSString *)foo
{
    return [Derived foo];
}
@end

Finally, you could make AnotherDerived inherit from Derived as others have pointed out.

Answer 2

If I understand correctly, your Derived implements P , and your AnotherDerived is supposed to call foo implemented in Derived ? You need to make AnotherDerived inherit from Derived :

@interface AnotherDerived: Derived
- (NSString *)foo
{
    return [super foo];
}

No need to make AnotherDerived implement P , because Derived already does that.