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iOS

Alex Atwater
Alex Atwater
2,624 Points
Posted by Alex Atwater
Alex Atwater
2,624 Points

super init method

in this video: http://teamtreehouse.com/library/build-a-blog-reader-iphone-app-2/data-modeling/designated-initializers-and-convenience-constructors-2 at around 7:50, Amit Bijlani did this:

-(id) iniWithTitle(NSString *)title {

    self = [super init]
}

so he is in the class of BlogPost, yet as far as i know, which is why i'm confused, he is initializing it with the super class, which is NSObject. So if he initializes self, an instance of BlogPost with the NSObject initializer, a) isn't it an instance of NSObject and b) if it is an NSObject, how can it access self.title if self.title is a property of BlogPost if its not initialized that way?

2 Answers

Amit Bijlani
STAFF
Amit Bijlani
Treehouse Guest Teacher
Amit Bijlani
Amit Bijlani
Treehouse Guest Teacher

That is a really good question and has a very complicated answer which can be found in this article: http://www.cocoawithlove.com/2009/04/what-does-it-mean-when-you-assign-super.html

Stone Preston
Stone Preston
42,016 Points
Stone Preston
Stone Preston
42,016 Points

That is some difficult stuff to understand right there. Anyway you could explain it in simpler terms Amit Bijlani

John W
John W
21,558 Points
John W
John W
21,558 Points

Objective-C's alloc-init pattern, which handles alloc and init separately, is not to be confused with C++ or Java's constructor pattern, which conceptually bundles both alloc and init in one call.

At the high level, the allocation of the required properties and ivars are done and made available during alloc. The purpose of init is to initialize everything such as variables with initial values. Your superclass's init initializes everything common among all subclasses, but it is still allocated and synthesized as your subclass in the part where you called [YourClass alloc]. Hence if you do nothing in your own init but [super init], your own properties such as title will be available since they are allocated by alloc, but they won't be initialized and hold the default value nil