Share code between classes in Objective-C without inheritance?

Since Objective-C does not support multiple inheritance, is there some other mechanism to share code between classes?

I'm writing a Cocoa library on top of an existing xml schema. Many elements in the schema (for example, ) are used in multiple types. I was hoping to centralize this somehow, so that I didn't have to add @property NSString *name and the associated code to generate the xml for the name property in every single class that has a name attribute. That would be fairly straightforward if multiple inheritance were supported, but I don't know how to do it otherwise.

The best thing I can think of is to create a common superclass that has a superset of methods to encode each optional property, then call the appropriate methods (i.e. encodeName) in the encoding method for each class. 开发者_高级运维Does that seem like the best way to go?

I would recommend you create a new Category with your properties/functions etc and add said category to NSObject. That would make all properties and functions available to all subclasses of NSObject. It's not exactly multiple inheritance but provides a great amount of flexibility.

It is actually possible to add data to a class at run time using the runtime's Associative Reference functions. It's a little deeper than normal SDK work, but works quite well. It's not the same as a full property with getters and setters, but it does associate objects with an instance.

If the methods are only required on certain objects then maybe a sub class from that class is the way to go or a category on that specific class would be better. The category on NSObject is quite a wide net to cast.

If you want to add additional state then sub classing is probably your safest bet.

If you do add a category make sure you prefix your methods with something unique so to avoid any conflicts. E.g. PSMySpecialMethod as opposed to mySpecialMethod