Objective-C best practice for using class methods

Question

I am used to functional programming. Now writing for iOS I find myself using class methods (+) frequently, rather than creating instances (from -).

Usually I use class methods for small, recurring tasks - like sending async requests, updating database, storing/retrieving preferences etc.

Is this the right thing to do, or should I try to change my thinking more and start using instances instead? Is it even possible to avoid using class methods all together?

If you can't stop yourself from using only C, there is a way (though it is not recommended) you can get an [app up and running](http://stackoverflow.com/questions/10289890/how-to-write-ios-app-purely-in-c). — CodaFi, Mar 03 '13 at 17:20
@RichardJ.RossIII Says the one that's trolling month-old questions ;) — CodaFi, Apr 17 '13 at 21:44

score 4 · Accepted Answer · answered Mar 03 '13 at 17:11

My best recommendation would be to look at how Foundation and Cocoa is doing and do it similarly. There is a place for class methods in Objective-C.

Some examples of class methods include

[UIView animateWithDuration:0.3 animations:^{
    // Animation here...
}];

and

[NSURLConnection sendAsynchronousRequest:request
                                   queue:[NSOperationQueue mainQueue]
                       completionHandler:^(NSURLResponse *response, NSData *date, NSError *error) {
                           // Handle response here ...
                       }];

Those are more of convenience methods and initializers (especially the animation one) than tried and true class methods, but I see your point. +1 — CodaFi, Mar 03 '13 at 17:16

score 2 · Answer 2 · answered Mar 03 '13 at 17:08

There is a third alternative supported by Objective C for encapsulating functionality that does not need implicit access to instance variables - it is using "plain" C functions. Unlike class functions, "plain" C functions do not use virtual dispatch, which may be important in vary tight loops.

Note that class methods provide more functionality than, say, static methods of Java, C++, and C#: they support overriding, letting class method in base classes use more specific implementations in derived classes.

score 0 · Answer 3 · answered Mar 03 '13 at 17:07

0

Class methods are used when you do not need any instance of the class, and your purpose gets served only by a method call of that like [[NSUserDefaults standardUserDefaults] synchronize];

In MRC

The alloc/init combination gives you an owning reference. That means you must release it later on. The classMethod returns a non-owning reference. You may not release it.

i.e.,

Person *firstPerson=[Person personWithName:@"AnoopVaidya" address:@"India"];

In ARC, for the above there is not such differnce.

answered Mar 03 '13 at 17:07

Anoop Vaidya

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I would say that class methods serve a far broader purpose than that. I can, for instance, make a little "singleton" out of a static variable and make the class method an accessor. – CodaFi Mar 03 '13 at 17:15
@CodaFi: Yes that should be in Answer :) – Anoop Vaidya Mar 03 '13 at 17:16

Objective-C best practice for using class methods

3 Answers3