How to write an RPG in Objective-C/cocoa

i would like to know some general things when it comes to writing a RPG. I have read the following article: RPG but the program is written in python and it only gives some ideas to what you can have inside your RPG.

What i want is to know what classes to us开发者_JAVA百科e. like NSView vs CALayer and so on...

I want it to be in 2D =)

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I haven't tried it myself, but I've heard good things about cocos2d.

It's a framework for 2d games, I think an RPG would work fine on it.