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I have a questions about the iPhone application. I am the green of the iPhone application. When I read the document(PDF) download from the apple developer website (online version). I found that the document always mentions different methods of the library.

There are

1) Class method

2) Instance method

3) Delegate method

I understand the use and meaning of the instance method, which is called by a instance.

let's say the delegate methods is the connection:didReceiveAuthenticationChallenge and the class method sendSynchronousRequest:retruningResponse:error:.

However, I don't understand about the different between the class method and the delegate method. Is the class method for the whole class? or whole project? What it means of the delegate? and where should I put the code after I modify the content of the delegate? How can I call the method?

Can anyone help me. Thank you very much.

It is another question about the delegate method. And I don't how to solve the problems. Please help me. Thank you. HTTP status code = 0 (iPhone) (objective c)

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3 Answers3

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Suppose you have a class Foo and an instance of that, Foo* foo.

Then, the class method is a method which is sent to the class:

     [Foo classMethod];

while the instance method is a method sent to the instance:

     [foo instanceMethod];

The delegate method is a method which the instance of the class calls. So, you typically implement another class Delegate with an instance Delegate* delegate, and do

    [foo setDelegate:delegate];

Then, the object foo calls the delegate method of delegate at appropriate times:

    [delegate delegateMethod];

This is a way to receive an event from the system API.

Yuji
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  • thank you for your reply. Do you mean that I have to create a new class (.h & .m)? or just declare the class within the .m. As I have write some code in the delegate method, i don't know what to call it. For example, my class is call 'classA', what should I do? – Questions Jul 06 '10 at 03:36
  • You implement the delegate methods in your delegate. – Yuji Jul 06 '10 at 03:40
  • I add the code "NSURLConnection *theConnection = [[NSURLConnection alloc] initWithRequest:request_get2 delegate:self];" to my program, but I still display the error. I add the NSLog to the "canAuthenticateAgainstProtectionSpace" and "didReceiveAuthenticationChallenge". However, they display the NSLog message after the error message. Is there are any problems? – Questions Jul 06 '10 at 04:10
  • Do you think I'm a psychic? If not, please write what was the error! Thank you. – Yuji Jul 06 '10 at 04:19
  • Please don't add a comment with the error below this comment; instead, revise your original question above! – Yuji Jul 06 '10 at 04:21
  • @mark: Could you please decide wether you want to know about the concepts of methods/delegates or wether you want help on some concrete problem? You can always open a seperate question on the specific implementation problem you are having. – Georg Fritzsche Jul 06 '10 at 04:37
  • thank you for everyone. forget me as a green for this website. I just want to ask the following up questions. I have posted the code and error message to this post. Please see the modified post on the above. There is a link to question. Thank you. – Questions Jul 06 '10 at 05:36
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Apple provides extensive documentation on the fundamentals for Objective-C and Cocoa - if in doubt, this should be your first stop.

The Objective-C Programming Language - Class Objects:

[...] a class definition can include methods intended specifically for the class object—class methods as opposed to instance methods. A class object inherits class methods from the classes above it in the hierarchy, just as instances inherit instance methods.

Cocoa Fundamentals Guide - Delegates and Data Sources:

A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program.
The delegating object is often a responder object—that is, an object inheriting from NSResponder in Application Kit or UIResponder in UIKit — that is responding to a user event. The delegate is an object that is delegated control of the user interface for that event, or is at least asked to interpret the event in an application-specific manner.

And some related background in The Objective-C Programming Language - Protocols:

Class and category interfaces declare methods that are associated with a particular class — mainly methods that the class implements. Informal and formal protocols, on the other hand, declare methods that are independent of any specific class, but which any class, and perhaps many classes, might implement.

Georg Fritzsche
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A delegate method is a method that is defined in a classes delegate protocol. They are added to your class but your class must have the objects delegate protocol. They are usually used by the object but is something that you must define for the object. NSTableView and UITableView use delegate methods to populate their data. A class method is just one that you define in your interface.

Conceited Code
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  • Thank you for your reply. I want to ask what is a 'classes delegate protocol'? What is the 'objects delegate protocol'? Also,if I want to use the delegate, how can I use it? thank you. – Questions Jul 06 '10 at 03:21
  • Sorry. I am still new to SO. These are some really complicated topics. The apple documentation is great, but can be hard to understand if you are new. Georg gave some great references. I will write some blog posts about these topics with in the next week. I will try to make these as easy as possible to understand. – Conceited Code Jul 06 '10 at 04:14
  • Fair enough, updating the answer in response to comments works e.g. fairly well if you can't fit it into comments :) – Georg Fritzsche Jul 06 '10 at 04:42