问题:

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.

回答1:

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.

回答2:

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
}
}

回答3:

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.