在iOS我们都知道注册完通知后，都要移除通知，配对使用。

那在ReactiveCocoa中如何正确的使用通知，我们可以通过RAC()和-takeUntil:达到结束消息，移除通知。

// Stops observing the notification when `self` is deallocated.
RAC(self.latestObject) = [[NSNotificationCenter.defaultCenter
    rac_addObserverForName:GimmeDatObjectNotification object:nil]
    map:^(NSNotification *notification) {
        return notification.userInfo[DatObjectKey];
    }];

// Stops observing the notification when `cancelSignal` sends next or completed.
[[[NSNotificationCenter.defaultCenter
    rac_addObserverForName:SomeNotification object:nil]
    takeUntil:cancelSignal]
    subscribeNext:^(id x) {
        @strongify(self);
        NSLog(@"UPDATE UPDATE");
    }];