correct kvo observe value for key path

kvo

// in the initializer, or viewWillAppear,etc:

[self addObserver:self forKeyPath:keyPath options:options context:(__bridge void*)self];

// in dealloc, or viewDidDisappear, etc:
[self removeObserver:self forKeyPath:keyPath context:(__bridge void*)self];


- (void) observeValueForKeyPath: (NSString *) keyPath ofObject: (id) object change: (NSDictionary *) change context: (void *) context {
    if ((__bridge id)context == self){
        if ([[change valueForKey:NSKeyValueChangeNotificationIsPriorKey] isEqual:@YES]){
            // willChange, etc.
        } else {
            // didChange, etc.
        }
    } else {
        [super observeValueForKeyPath: keyPath ofObject: object change: change context: context];
    }
}