CODEWITHSUNDEEP
iphoneios
js_
js_

Reputation: 4731

In iPhone, is it guaranteed that viewWillAppear, viewDidAppear, viewWillDisappear, viewDidDisappear are always called?

I'm using viewWillAppear, viewDidAppear, viewWillDisappear, viewDidDisappear of UIViewController.
And I use UINavigationController to navigate view controllers.

For example, I create NSTimer or register notifications in viewWillAppear or viewDidAppear. And I invalidate the timer or remove notifications in viewWillDisappear or viewDidDisappear.

But if those 4 methods (viewWillAppear, viewDidAppear, viewWillDisappear, viewDidDisappear) are not called, the program will crash or retain cycle will happen.

I couldn't find the documentation saying that it is guaranteed that viewWillAppear, viewDidAppear, viewWillDisappear, viewDidDisappear are always called.

Till now, they seem to be always called and my program works as I expected.

But are there cases that the 4 methods are not called?
Or is it possible the 4 methods are usually called but sometimes not called randomly with no reason?

Upvotes: 0

Views: 2929

Answers (6)

Sea Coast of Tibet
Sea Coast of Tibet

Reputation: 5081

Aside from bugs when some of the methods may not get called and/or called twice (e.g. dismissing/popping several controllers at once), with iOS 7, if you initiate the swipe-to-back gesture, partially revealing the previous controller in the navigation stack, and then cancel the swipe-to-back, so that no popping occurs, you will observe that not all of the methods get called on both of the controllers.

Upvotes: 0

Dmitry Zheshinsky
Dmitry Zheshinsky

Reputation: 569

I can say than viewWillAppear and viewDidAppear methods are always called in your view. viewWillDisappear and viewDidDisappear methods are called when you change your view with another one or close it. If you have some scrolling views for example, these methods won't be called.

Upvotes: 3

Michael Mior
Michael Mior

Reputation: 28753

Yes, they are always called. Just make sure to call the superclass implementation if you subclass one of your view controllers.

Upvotes: 2

IsakBosman
IsakBosman

Reputation: 1533

Yes the View events always fire, however to override the behaviour you must declare them.

According to apple documentation viewDidUnload is deprecated.

Look at this link for the official apple class reference for UIViewController

UIViewController Reference

It states:

The UIViewController class provides specific methods that are called when these events occur. Subclasses can override these methods to implement specific behaviors.

Upvotes: 1

Rui Peres
Rui Peres

Reputation: 25907

I think you can trust those methods, still, viewDidLoad and dealloc for me never failed.

You can register and remove notifications there. But, I don't know all of your app specifications and what I recommend might not be viable.

Upvotes: 1

Mohammad Kamar Shad
Mohammad Kamar Shad

Reputation: 6067

Here are the same thread in which same thing asked m any times you can view these here

here the first link

here the second one

Upvotes: 0

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