I noticed that Cocoa/Objective-C classes inherit and conform from other classes. I understand what inheritance is, but not conformance. What's the difference?
Also, is a class like UIView a Cocoa class or an Objective-C class?
+1
A:
Conformance or more accurately conforming to a protocol is simply Objective C's way of specifying behavior that the class should implement, similar to a java interface.
UIView is part of the UIKit framework so it is a Cocoa class.
ennuikiller
2010-07-30 23:32:05
No, UIView is part of the UIKit framework, so it is a *Cocoa Touch* class. UIKit is not part of Cocoa.
Peter Hosey
2010-07-30 23:50:40
Yes, I stand corrected....
ennuikiller
2010-07-31 00:59:57
A:
Conformance is more or less the same as assignability. But i never saw this second term used used for it.
If you can assign an object to a variable b then a conforms to b.
Lothar
2010-07-30 23:51:06
Except that in Objective-C, you can assign a pointer to an instance of any class to any pointer variable, including a variable declared as holding a pointer to an instance of a completely unrelated class.
Peter Hosey
2010-07-31 01:37:29
+1
A:
Classes don't conform to classes, they conform to protocols, which are basically lists of messages that a class can respond to. If a class conforms to a protocol, it must respond to all the non-optional messages listed in the protocol interface.
Also, there isn't really a difference between a Cocoa class and an Objective-C class. Cocoa is an Objective-C framework, so all of its classes are Objective-C classes. If you're asking whether classes like UIView are part of the language or the framework: Every class you normally interact with in a Cocoa/Cocoa Touch app comes from the framework. The native classes the standard Objective-C runtime provides are:
- Object
- Protocol
- List
You can go to /usr/include/objc if you want to see the headers for yourself. None of these are used in a normal Cocoa or Cocoa Touch program. You do use Protocols (as mentioned above), but don't normally refer to the class directly.
Chuck
2010-07-30 23:57:35
I've seen things conform to NSObject. Isn't that an object and not a protcol?
awakeFromNib
2010-08-01 21:51:39
@awakeFromNib: It's both. There is an NSObject class and a protocol named NSObject to which the class conforms. Class: http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html Protocol: http://developer.apple.com/mac/library/documentation/Cocoa/Reference/Foundation/Protocols/NSObject_Protocol/Reference/NSObject.html#//apple_ref/occ/intf/NSObject
Chuck
2010-08-01 22:05:32