Subclassing initialize method in objective-c

Question

I have a class Foo that implements an +(void)initialize method. I also have a class that's a subclass of Foo. When I instantiate the subclass, the initialize method also gets called on Foo which I don't want. How do I prevent this?

Thanks.

Am I right in thinking you just don't do self = [super init] in the subclass init method? — petert
– petert, Commented Jan 18, 2012 at 16:48
I think he is talking about the class initialize method, but if he is really referring to init, then that is correct. — Peter DeWeese
– Peter DeWeese, Commented Jan 18, 2012 at 16:51

Costique · Accepted Answer · 2012-01-18 18:25:04Z

7

In your scenario (when there are subclasses involved) you should check the class to which the initialize method is sent:

+ (void) initialize
{
    if ( self == [MyClass class] )
    {
        // Do something here only once
    }
}

answered Jan 18, 2012 at 18:25

Costique

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Comments

Peter DeWeese · Accepted Answer · 2012-01-18 17:22:08Z

1

You'll need to implement + (void)initialize in your subclass as well. Usually people call [super initialize], but you'll want to skip that step. An empty method will prevent Foo's from being called.

EDIT The superclasses initialize method is always called. It can't and shouldn't be prevented by subclassing, because technically the superclass is initialized too and could be used independently.

edited Jan 18, 2012 at 17:22

answered Jan 18, 2012 at 16:49

Peter DeWeese

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4 Comments

JPC Over a year ago

I implement initialize in BOTH my subclass and superclass. According to the apple docs, the superclass's initialize will always get called before any subclasses. Is there anyway to prevent that

Peter DeWeese Over a year ago

Huh. I tested it out and see the same thing. I think I'm changing my answer. What is Foo's initialize method doing that you must prevent?

JPC Over a year ago

It alloc-inits an object that listens for and acts on notifications in a way different to how its subclass does it. I've solved it by not implementing initialize and just calling a setup method instead.

Peter DeWeese Over a year ago

Sounds like a reasonable solution.. It probably didn't belong in initialize in the first place. Please add your answer and accept it when allowed.

JPC · Accepted Answer · 2012-05-08 18:08:33Z

0

I've solved it by not implementing initialize and just calling a setup method instead

answered May 8, 2012 at 18:08

JPC

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2 Comments

fishinear Over a year ago

Costique's answer is better, and also the recommended way by Apple. Calling a setup method only once can be surprisingly difficult in the presence of multiple threads, and initialize is made for that purpose.

Steven Kramer Over a year ago

Fishinear, bbum says otherwise and is usually right (friday.com/bbum/2009/09/06/…)

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