KVO Context Pattern

FOOClass.m

static void *kFOOClassKVOContext = &kFOOClassKVOContext;

@implementation FOOClass

- (void)addKVOObservers
{
    [self.property addObserver:self forKeyPath:@"someKeyPath" options:0 context:kFOOClassKVOContext];
}

- (void)removeKVOObservers
{
    [self.property removeObserver:self forKeyPath:@"someKeyPath" context:kFOOClassKVOContext];
}

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if (context == &kFOOClassKVOContext) {
        // do stuff
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

@end