领域令牌有什么用？

Question

When initialising a Realm notification, it's required to set a token:

// Observe Realm Notifications
__weak typeof(self) weakSelf = self;
RLMRealm *realm = [RLMRealm defaultRealm];
self.token = [realm addNotificationBlock:^(NSString *note, RLMRealm * realm) {
    [weakSelf updateUI];
}];

I'm not 100% clear for what this is good for. Is is to keep a reference to self?

Answer 1

I found possible answer: the token is required to remove the notification from a view. With the notification there seem to be no reference to it.