Calling "super init" in Objective-C [duplicate]

Question

This question already has answers here:

Why should I call self=[super init] (6 answers)

Closed 8 years ago.

While reading about classes in Objective-C I found that in some cases people advice that when implementing the init method to do it as:

- (id) init {

    if ( self = [super init] ) { 

        ...
    }

    return self; 
}

While others don't refer this. Which one is correct one?

Also, when defining setters most of the times they simply consist in an assignment but sometimes they appear as:

- (void) setCaption: (NSString*)input {

  [caption autorelease];
  [input retain];
  caption = input;
}

Once again, which one is the best approach? Does ARC has some effect on this? If I use ARC, I don't need to use autoreleaseas above?

thanks!

Answer 1

Straight from Apple's official documentation:

There are several critical rules to follow when implementing an init... method that serves as a class’s sole initializer or, if there are multiple initializers, its designated initializer (described in “Multiple Initializers and the Designated Initializer”):

• Always invoke the superclass (super) initializer first.

• Check the object returned by the superclass. If it is nil, then initialization cannot proceed; return nil to the receiver.

• When initializing instance variables that are references to objects, retain or copy the object as necessary (in memory-managed code).

• After setting instance variables to valid initial values, return self unless:

  • It was necessary to return a substituted object, in which case release the freshly allocated object first (in memory-managed code).

  • A problem prevented initialization from succeeding, in which case return nil.

---

Concerning the second issue, you typically don't have to implement the accessor methods by hand, but in case you must or want, here's a useful reference: Explicit getters/setters for @properties (MRC)

Answer 2

1

In general: call super.

But pay attention to dedicated initialiser and don't blindly override stuff

see: http://macdevelopertips.com/objective-c/objective-c-initializers.html

2

if you use arc, you don't have to do manual memory management so the setter would be one line. Most of the time auto-synthezing it is fine

Answer 3

I know that a reason calling [super init] is to actually initialize something belong to super class. I found a better answer given by @gabrielePetronella while I wrote my answer. Please check that out.

And, If you use ARC, you don't use a set of memory management methods such as [release], [autorelease]. Even though you try to use those methods, Xcode sends you a compile error.