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iPhone Objective-C foreach design question

Answer 1

+9 A:

You need to test for the class type:

for (Touch *t in touches) {
  if ([t isKindOfClass:[MoveTouch class]]) {
    MoveTouch *mt = (MoveTouch *)t;
    // do what you want with mt
  }
}

Louis Gerbarg 2009-11-10 07:26:06

Answer 2

A:

I'm not an Objective C programmer.

In your case, I think you need to go through your list with that "for (Touch* in touches)" and in the body figure out if that object is either a MoveTouch or a JumpTouch and so forth.

But the idea of polymorphism is that you don't do this. You don't sort 'm out during your loop. The action that you want to perform should be defined in the interface, and each descendant class implements a different implementation for that action. That's what polymorphism is all about.

Dave Van den Eynde 2009-11-10 07:27:29

... which means you would do something like call [t update] and then each item would decide what to do at an update cycle. But that's not universal. There are plenty of times when you have a message you want to send to one class, and not another.

Kenny Winker 2009-11-10 07:34:48

not universal, but does tend to smell, in my opinion. Especially when you indicate that you're designing the classes themselves as well.

Dave Van den Eynde 2009-11-10 10:21:52

I'm actually not doing polymorphism with this. My basic want was for a way to separate different kinds of touches. The kind of touch (Move, Jump, Interface, etc.) can be decided immediately upon its creation, which happens within "touchesBegan". From then on, it's much easier to separate the functionality of what happens when you MOVE that touch or END that touch, etc. I guess maybe inheritance is a little fancy for this? Maybe just a simple enum would work?

Scott 2009-11-10 15:59:28

Why yes, if you don't want polymorphism then inheritance is a bit overkill. A simple enum would avoid the whole runtime type checking, which is probably a lot less efficient.

Dave Van den Eynde 2009-11-10 18:40:18

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