I’ve finally started using ReactiveCocoa, it was about time!

I just want to share how I used it to parallelize a bunch of network requests, and to notify the user when they’re done.

This approach shows two possible ways to use ReactiveCocoa: signals combination, and collection magic.

- (void)viewWillAppear:(BOOL)animated {
  [super viewWillAppear:animated];

  [self showLoadingSpinner];
  [self getFeesForAllItemsWithCompletion:^{
    [self hideLoadingSpinner];

- (void)getFeesForAllItemsWithCompletion:(void (^)())completion {
  NSArray *signals = [self.allItems.rac_sequence map:^id(Item *item) {
    return [self getFeeForItemSignal:item];

  [[RACSignal combineLatest:signals] subscribeCompleted:completion];

- (RACSignal *)getFeeForItemSignal:(Item *)item {
  return [RACSignal startEagerlyWithScheduler:[RACScheduler scheduler] block:^(id<RACSubscriber> subscriber) {
      [APIClient getFeeForItemUUID:item.UUID
                           success:^(Fee *fee) {
                             [subscriber sendCompleted];
                           failure:^(NSError *error) {
                             [subscriber sendCompleted];

The code above is probably nothing exciting if you’re a RecativeCocoa PRO, but I’m quite pleased with it.

  • It uses map to transform an array of Item into one of RACSignal.
  • The signal creation is encapsulated in it’s own method, making the code more readable.
  • The method that performs the signal combination receives a completion callback object, rather than doing it itself. This makes it reusable and single purpose.

Food for thought

  • Is this a proper use of ReactiveCocoa? Or is there any best practice or pattern to achieve this in a better way?
  • How would this look in Swift 1.2 and ReactiveCocoa 3?
  • How would this look in Swift 2 and ReactiveCocoa 3? Any difference?