Question

Is there a lower level of API below Cocoa as Win32 API below MFC? If there is, Is it widely used in Mac OS X or iOS Application develepment?

Answer 1

CoreFoundation is the lower level C APIs:

http://developer.apple.com/corefoundation/

Foundation classes is the higher objective-c foundation set of classes:

http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/ObjC_classic/_index.html

Apple offers ‘toll-free’ bridging of types between these:

http://developer.apple.com/library/ios/#documentation/CoreFoundation/Conceptual/CFDesignConcepts/Articles/tollFreeBridgedTypes.html

For OSX AppKit (Cocoa) is the higher level UI framework which uses the foundation classes:

http://developer.apple.com/library/mac/#documentation/Cocoa/Reference/ApplicationKit/ObjC_classic/_index.html

For Devices (iOS), there’s UIKit (Cocoa Touch) over the foundation classes:

http://developer.apple.com/library/ios/#documentation/uikit/reference/UIKit_Framework/_index.html

All of these are widely used in OSX and iOS development …