Question

When creating a UIViewController derived class in objective-C, what goes into the init method, what should go into loadView and what into viewDidLoad – and more importantly why, and what benefit (performance?) does this have?

Also, how does this relate to UIView derived classes where the only option you have is the init method?

I know the template code already has comments for what goes into each method, but it unclear to me why each thing goes where they say.

Clarification

I would like to know maybe at a lower level, what is the actual difference between things being done in the ‘init’, ‘loadView’ and ‘viewDidLoad’. What does the framework do in between these calls that may affect the way/time I set up my views and do other work? How are these methods affected by threading?

Answer 1

You want to know some lower-level stuff.

init: This method gets called on ANY NSObject subclass. It is what sets up the object, which you probably already know. In many model (as in the MVC pattern) classes, init is directly used. As for the UIKit classes, very few requires init to be called directly. It should not be used. In the UIViewController, you initialize it using initWithNibNamed:. You can override this method, but in most cases this is not needed. This method is the VERY first method to EVER get called on the class (before any view setup, or such).

loadView:and viewDidLoad: read this article iPhone SDK: what is the difference between loadView and viewDidLoad? .

The only really important thing to know is that -init is the NSObject standard initialization method. -loadView and -viewDidLoad are UIViewController’s methods for initialization.