Question

I am a C# developer getting started on Objective-C / Cocoa Touch programming. I think I might have gotten some terms wrong because I keep thinking about them “the C# way”.
Specifically, I have come around the term “protocol” in various documentation and tutorials.

In Objective-C, what exactly is a protocol ? Can it be compared to a C# interface ?

Is the following declaration the same as saying “The class is implementing the protocol UITextFieldDelegate” ? Or is UITextFieldDelegate to be compared with a generic type parameter in C# ?

@interface MyViewController : UIViewController <UITextFieldDelegate> { }

Answer 1

In Objective-C a protocoll is the name for a collection of selectors/methods and is like an interface declaration in Java (probably also in C#).

@interface MyViewController : UIViewController <UITextFieldDelegate> { }

means that the class MyViewController inherits from the class UIViewController and adopts/implements the protocol UITextFieldDelegate.

This means that MyViewController must implement all methods declared in the UITextFieldDelegate.

EDIT: It seems that with the introduction of Objective-C 2.0 the possibility to mark methods of a protocol as @optional and @required was introduced.
See section Optional Protocol Methods of Apples Objective-C documentation.

Helpful link from wikibooks about Objective-C Protocols.