When should I call super?

Question

What is the best using of [super ... any method name]. Recently I have found out that In dealloc the [super dealloc] must stand in the same end. Because any variable what didn't use before can be filled by garbage if we set it after [super dealloc] It's a rare thing, but it's possible. After this we will have crash in our app. So what is the best using of super method, for example what is best using for -(void)viewWillAppear:(BOOL)animated. Where is the best place for [super viewWillAppear:(BOOL)animated] in the begin of body or in the end? Thanks.

Answer 1

The usual rule of thumb is that when you are overriding a method that does some kind of initialization, you call super first and then do your stuff. And when you override some kind of teardown method, you call super last:

- (void) setupSomething {
    [super setupSomething];
    …
}

- (void) tearDownSomething {
    …
    [super tearDownSomething];
}

The first kind are methods like init…, viewWillAppear, viewDidLoad or setUp. The second are things like dealloc, viewDidUnload, viewWillDisappear or tearDown. This is no hard rule, it just follows from the things the methods do.

Answer 2

It mostly depends on whether your subclass needs things to happen before the superclass method, or after. Or both, as the case may be.

That's why init methods call the super method first thing, and dealloc methods last thing. In your example, when you are being notified that a view will appear, you might want to let the super do its thing, and then, after that, take care of whatever your subclass view needs to do. But it could conceivably be other way around, or you could call the super method in between your code. Different rules will apply according to your application's needs.