CODEWITHSUNDEEP
objective-cdesignated-initializer
JDD
JDD

Reputation: 1

Objective-C: minimal init versus init that calls initWith?

The method init in most classes does a minimal initialization, because if you need more complexity, more has-a related behaviors, then you need to use an initWith method. So why would anybody call an initWith from within the init method? I have seen this, it's even mentioned on Apple's website, but it seems to conceal behaviors that should be explicitly named.

Upvotes: 0

Views: 136

Answers (1)

EmilioPelaez
EmilioPelaez

Reputation: 19892

Objects have what is called a "designated initializer", which are (there can be multiple) the init... methods that should completely initialize and configure the object for use.

Using a UIView as an example, it's designated initializer is initWithFrame:CGRect. This initializes the view with a frame (duh).

If init was the designated initializer, it would still have to define a frame, probably CGRectZero, and initWithFrame: would have to call init and then setFrame:, which means setting the frame twice. We don't like doing things twice when they can be done once.

That's why in many cases init is used instead as a shortcut when the properties in the other initializers can have a default value, usually some kind of zero. In the case of CGRect, CGRectZero is the zero-value.

Also, since frame is an important property of UIView, if your designated initializer was init, you'd see a lot of this:

UIView *view = [[UIView alloc] init];
view.frame = CGRectMake(0, 0, 20, 20)

It just makes sense to combine those two lines into one, that's why initWithFrame: is the designated initializer.

Upvotes: 4

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