Omit [super] call when overriding view events in UIViewController. Impact? [duplicate]

Question

This question already has answers here:

What is meaning of calling superview's viewwillappear? (3 answers)

Closed 8 years ago.

What happens if you don't call super in your implementation of the view events (viewWillAppear, viewDidAppear etc.) of UIViewController?

It seems like I've forgotten to do this before, and it's unclear to me that there was any adverse impacts.

Answer 1

If you subclass one of your own view controller classes, you will certainly want to call super for any of these types of methods or your own base class's methods will not be invoked.

There's also the question of whether your top-level view controller classes need to call super to run the code in the base UIViewController class itself. In the UIViewController reference, it appears that the requirement to call super is documented for certain methods, among them viewWillAppear:, viewDidAppear, viewWillDisappear:, and viewDidDisappear:

If you override this method, you must call super at some point in your implementation.

However, there is no indication of what will happen if you fail to do so.

So apparently, there is something implemented in these methods in the base iOS framework view controller classes. Or at least, Apple reserves the option to implement something in these methods. You could say that they are virtual rather than abstract methods.

Answer 2

If you've subclassed your UIViewController delegate from anywhere (and you always subclass UIViewController at least once, in making your customized view controller), then any delegate methods in subclasses you've derived from won't get called.