iOS Architecture - Cocoa Stack

APP

Cocoa Touch - UIKit

Media

Core Services - Foundation

Core OS


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Link:
http://www.cnblogs.com/kkun/archive/2012/04/25/2470166.html


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UIKit:
Prefix: UI
Examples: UIApplication, UIWindow, UIScreen, UIView, UIViewController...etc.

Foundation:
Prefix: NS
Examples: NSData, NSDate, NSInteger, NSArray, NSLog, ...etc.