How to use Reactive Cocoa with notifications

Question

How can I create a signal out of a notification name? For example, I want to go from:

[[NSNotificationCenter defaultCenter] addObserver:self
                                         selector:@selector(userDidChange:)
                                             name:kTTCurrentUserLoggedOffNotification
                                           object:nil];

to something like:

[signalForName(kTTCurrentUserLoggedOffNotification) subscribeNext:^(id x){
...
}];

Answer 1

-[NSNotificationCenter rac_addObserverForName:object:] returns an infinite signal. You can subscribe to it like this

Objective-c

[[[[NSNotificationCenter defaultCenter] rac_addObserverForName:UIApplicationDidEnterBackgroundNotification object:nil]
  takeUntil:[self rac_willDeallocSignal]]
  subscribeNext:^(id x) {
     NSLog(@"Notification received");
}];

Swift

NSNotificationCenter.defaultCenter()
  .rac_addObserverForName(UIKeyboardWillShowNotification, object: nil)
  .takeUntil(self.rac_willDeallocSignal())
  .subscribeNext { (_) in
     print("Notification received")
  }

---

This signal is as stated infinite. If you need this signal/subscription to be bound to the lifetime of self you can add takeUntil: with rac_willDeallocSignal like this:

Objective-c

[[[[NSNotificationCenter defaultCenter] rac_addObserverForName:UIApplicationDidEnterBackgroundNotification object:nil]
  takeUntil:[self rac_willDeallocSignal]]
  subscribeNext:^(id x) {
     NSLog(@"Notification received");
}];

Swift

NSNotificationCenter.defaultCenter()
  .rac_addObserverForName(UIKeyboardWillShowNotification, object: nil)
  .takeUntil(self.rac_willDeallocSignal())
  .subscribeNext { (_) in
     print("Notification received")
  }

Answer 2

In the RACExtensions you can find the NSNotificationCenter (RACSupport) category. That has a method for this purpose:

- (RACSignal *)rac_addObserverForName:(NSString *)notificationName
                               object:(id)object;