Comments on: Introduction to Protocols

By: John Muchow

John Muchow — Sat, 17 Sep 2011 19:16:39 +0000

Thanks Bowen, I really appreciate the kind words!

By: Bowen

Bowen — Sat, 17 Sep 2011 06:37:12 +0000

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By: Frank V.

Frank V. — Thu, 21 May 2009 14:09:29 +0000

Eric, you are right.

Ref: http://developer.apple.com/documentation/Cocoa/Conceptual/ObjectiveC/Articles/ocObjectsClasses.html#//apple_ref/doc/uid/TP30001163-CH11-SW3

By: Eric Lloyd

Eric Lloyd — Thu, 21 May 2009 03:23:44 +0000

dax,

I just spent some time fighting with this, trying to get the syntax right amid myriad unhelpful compiler messages. Correct me if I’m wrong (I don’t have my code in front of me right now), but I believe the “*” in “id *fubar” should not be there, since id is already by definition a pointer.

By: Frank

Frank — Wed, 15 Apr 2009 18:20:07 +0000

dax,

Thank you very much for taking the time to answer my question. It is clear that I don’t understand this part of Objective-C. Time to go to the book store. Again, thank you.

Regards,
Frank

By: dax

dax — Mon, 13 Apr 2009 22:17:58 +0000

Another option, use the object placeholder “id” along with ‹Fubar›, to typecheck that you want any object that conforms to Fubar protocol:
id ‹Fubar› *fubar = [[AnotherClass alloc] init];

By: dax

dax — Mon, 13 Apr 2009 22:14:30 +0000

[Regarding your question, Frank...]

Your example would attempt to make a Fubar class pointer called fubar and point it at AnotherClass instance, which shouldn’t work as no Fubar class was defined

To explicitly check if the class conforms to Fubar you can use conformsToProtocol:
if ([AnotherClass conformsToProtocol;@protocol(Fubar)]) {
AnotherClass *fubar = [[AnotherClass alloc] init];
}

Another option, use the object placeholder “id” along with , to typecheck that you want any object that conforms to Fubar protocol:
id *fubar = [[AnotherClass alloc]init];

If AnotherClass doesn’t conform to Fubar then you will receive a compiler error

By: Frank

Frank — Mon, 06 Apr 2009 21:09:12 +0000

So, a question if you don’t mind. You said that protocols are analogous interfaces which is what I thought.

Since this is true, does that mean that the polymorphism works the same way on Protocols as they do as Java Interfaces? Using your Fubar example, could I do the following:

Fubar *fubar = [[AnotherClass alloc] init];


   int RetVal = [fubar status];

[fubar release]; //Also, would I have access to release ?

Please excuse the quick example and I’m sorry if the Objective-C isn’t quite right. I’m still learning it…

Thank you,
Frank