ObjectiveDDP + ReactiveCocoa

new.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [[[NSNotificationCenter defaultCenter] rac_addObserverForName:MeteorClientDidConnectNotification object:nil] subscribeNext:^(id x) {
    NSLog(@"connected to server!");
  }];
  
  [[[NSNotificationCenter defaultCenter] rac_addObserverForName:MeteorClientDidDisconnectNotification object:nil] subscribeNext:^(id x) {
    NSLog(@"disconnected from server!");
  }];
  return YES;
}

old.m

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reportConnection) name:MeteorClientDidConnectNotification object:nil];
  
  [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(reportDisconnection) name:MeteorClientDidDisconnectNotification object:nil];
  
  return YES;
}

- (void)reportConnection
{
  NSLog(@"connected to server!");
}

- (void)reportDisconnection
{
  NSLog(@"disconnected from server!");
}