CODEWITHSUNDEEP
ioscocoa-touchuikitnsnotificationcenter
Woodstock
Woodstock

Reputation: 22926

NSNotificationCentre Crash

In my Application I listen for keyboard notifications:

  [[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(keyboardWillShow)
                                             name:UIKeyboardWillShowNotification
                                           object:nil];

I have just removed a bug which caused a crash in my app,

I have a modal view with a UI (which gets destroyed and recreated each time it's presented.

I was getting a crash the second time I went to use it before I added this line of code:

[[NSNotificationCenter defaultCenter] removeObserver:self];

Any one know why not removing observer for a dealloced object caused a crash?

Upvotes: 4

Views: 302

Answers (3)

Dany Joumaa
Dany Joumaa

Reputation: 2040

NSNotificationCenter maintains references to objects that may or may not have been dealloc'd. The crash occurs the second time because NSNotificationCenter doesn't know that the old UIViewController has been totally released.

Upvotes: 1

user2666713
user2666713

Reputation: 200

This is because when you get the notification, if you havent removed your class as an observer, it still tries calling the method. However, since the object has been completely deallocated and destroyed, you get an EXC_BAD_ACCESS.

Upvotes: 3

David Elliman
David Elliman

Reputation: 1389

It is a good idea to remove any observers in the dealloc method for a class. Otherwise the notification is sent to an object that no longer exists, which crashes.

Upvotes: 1

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