Dealing with variable assignments and async requests

users = [MySingleton sharedInstance].users;

- (id)getUsersAndNotifyObject:(id)object selector:(SEL)selector

// register observer first so you don't miss an update
[[MySingleton sharedInstance] addObserver:self
                               forKeyPath:@"users"
                                  options:(NSKeyValueObservingOptionNew | NSKeyValueObservingOptionOld)
                                  context:&kvo_users_context];
 users = [MySingleton sharedInstance].users;

 // implement appropriate observeValueForKeyPath:ofObject:change:context: method

[[NSNotificationCenter defaultCenter] addObserver:self
                                          selector:@selector(sharedDataChanged:)
                                              name:MySingletonDataUpdatedNotification
                                            object:[MySingletonDataUpdatedNotification sharedInstance]];
 users = [MySingleton sharedInstance].users;

 // implement appropriate sharedDataChanged: method

users = [MyDataFactory getUsers];

@interface RecipeRepository {}
- (void)initWithDelegate:(id)aDelegate;
- (void)findAllRecipes;
- (void)findRecipeById:(NSUInteger)anId;
@end

@protocol RepositoryDelegateProtocol
- (void)repository:(id)repository didRetrieveEntityCollection:(NSArray *)collection;
- (void)repository:(id)repository didRetrieveEntity:(id)entity;
@end

- (void)viewDidLoad
{
  self.users = [MySingleton getUsers];
  [self.view setNeedsDisplay];
}

- (void)viewDidLoad
{
  if(self.repository == nil) { // just some simple lazy loading, we only need one repository instance
    self.repository = [[[RecipeRepository alloc] initWithDelegate:self] autorelease];
  }
  [self.repository findAllRecipes];
}

- (void)repository:(id)repository didRetrieveEntityCollection:(NSArray *)collection;
{
  self.users = collection;
  [self.view setNeedsDisplay];
}

@protocol RepositoryDelegateProtocol
- (void)repositoryWillLoadEntities:(id)repository;
@end

// in your controller

- (void)repositoryWillLoadEntities:(id)repository;
{
  [self showLoadingView]; // etc.
}