CODEWITHSUNDEEP
ioscocoa-touchkey-value-observingautomatic-ref-counting
drunknbass
drunknbass

Reputation: 1672

KVO and ARC how to removeObserver

How do you remove an observer from an object under ARC? Do we just add the observer and forget about removing it? If we no longer manage memory manually where do we resign from observing?

For example, on a view controller:

[self.view addObserver:self
            forKeyPath:@"self.frame"
               options:NSKeyValueObservingOptionNew 
               context:nil];

Previously, I would call removeObserver: in the view controller's dealloc method.

Upvotes: 87

Views: 20409

Answers (3)

user3461902
user3461902

Reputation: 79

I do it with this code

- (void)dealloc
{
@try{
    [self.uAvatarImage removeObserver:self forKeyPath:@"image" context:nil];
} @catch(id anException) {
    //do nothing, obviously it wasn't attached because an exception was thrown
}
}

Upvotes: 1

Elise van Looij
Elise van Looij

Reputation: 4232

Elsewhere on stack overflow, Chris Hanson advises using the finalize method for this purpose and implementing a separate invalidate method so that owners can tell objects that they are done. In the past I have found Hanson's solutions to be well-thought-out, so I'll be going with that.

Upvotes: -2

Brad Larson
Brad Larson

Reputation: 170319

You still can implement -dealloc under ARC, which appears to be the appropriate place to remove the observation of key values. You just don't call [super dealloc] from within this method any more.

If you were overriding -release before, you were doing things the wrong way.

Upvotes: 126

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