Objective-c using parent properties in init method

Question

I read that using properties in init method is considered as bad practice. But should I use parent class properites ?

For example

-(id) init
{
    if (self = [super init])
    {
        self.parentProp = someVal; // (1)
        parentProp = someVal; // (2)
    }

    return self;
}

What is prefered (1 or 2) and why? Thanks!

score 3 · Accepted Answer · answered Jul 12 '12 at 21:12

After you've called super's init method, and it has returned, the superclass's part of your object is initialized and ready for use. It's normal and expected that you use its property accessors after that. For example. If you make a subclass of UIViewController, it's normal to then set your (inherited) title property, or modify your navigationItem, in your init method.

That said, you can break this behavior. If you've overridden one of your superclass's methods (including one of its accessors methods), and then you call that method in your init method, it's up to you to be sure your overridden method will behave properly before your object is fully initialized.

More subtly, maybe you're overridden a superclass method, and then you call a different superclass method that you haven't overridden. Well, what if the method you call turns around and calls the method you have overridden? You need to be aware of this possibility too.

All that said, I reiterate that it's perfectly normal to use your superclass's property accessors to customize it after you have initialized it by calling one of its init methods.

So I can expect the full polymorphic behavior of my class in init method? (I'm asking because the language I'm most familiar with is c++, and you cane problems if calling virtual functions from constructors) — Andrew, Jul 13 '12 at 04:40
Yes, you always get the most-derived version of a method, except when you explicitly send a message to `super`. This is completely different from (and much simpler than) object construction in C++. — rob mayoff, Jul 13 '12 at 06:26

score 1 · Answer 2 · edited May 23 '17 at 12:31

To answer your question - neither of them.

(2) is not a property access, but direct instance variable access. It depends on the class hierarchy design, but in general I would strongly discourage from using ivars in non-private interfaces - for details, see this answer to related question
In general, you should not use any of the class public methods (including properties access) in the class initializer (and in the dealloc for that matter) - if you class hierarchy doesn't prohibit subclassing explicitly. Because if you do - the subclasses overriding these methods (or properties accessors) will get them called while being in invalid state (not yet initialized or already dealloc'ed).

While I've encountered a number of problems caused by pt.2 in general it seems to be a common practice to ignore it (i.e. to use self/parent class properties in initializer). So I would say it's up to you. Either write more code for explicit setup outside of your classes initializers and feel confident that you would never encounter this problem. Or have probably more simple/short initialization and easier usage of your class but stay aware of that problem.

Objective-c using parent properties in init method

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