Question

I was looking at the Pro Core Data examples and I was wondering what a good way to pass around the ManagedObjectContext is. In the examples in the book, I see the author initialize the ManagedObjectContext in the AppDelegate, then he does this in MasterViewController

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];
    if (self) {
    self.title = NSLocalizedString(@"League Manager", @"League Manager");
    id delegate = [[UIApplication sharedApplication] delegate];
    self.managedObjectContext = [delegate managedObjectContext];
    }
    return self;
}

Then when a new ViewController is pushed on the stack from a table row selection, this is done:

NSManagedObject *team = [[self fetchedResultsController] objectAtIndexPath:indexPath];
  TeamViewController *teamViewController = [[TeamViewController alloc] initWithMasterController:self team:team];
  [self presentModalViewController:teamViewController animated:YES];

Using StoryBoards, I don’t see that type of init method anymore. I see the prepareForSegue is mainly used and I see in the Beginning iOS 5 Development book, the author would do something like this:

- (void)prepareForSegue:(UIStoryboardSegue *)segue sender:(id)sender {
        UIViewController *destination = ((UINavigationController *)segue.destinationViewController).topViewController;

        if ([destination  respondsToSelector:@selector(setDelegate:)]) {
            [destination setValue:self forKey:@"delegate"];
        }

I can’t figure out a good way to keep my classes decoupled and have a reference to the managedObjectContext in my viewControllers. Do I have a managedObjectContext that I just set on all my view controllers that need to see it? Do I do what the author in the first example did and keep a reference to the MasterViewController that has the reference and pass that around to my different ViewControllers? I’m not sure what is “best practices” for something like this. Thanks!

Answer 1

prepareForSegue:sender: is indeed the preferred way to pass data from one view controller to another when using storyboards. The example prepareForSegue code you posted is exactly how you’d do it. I have exactly this code in one of my apps:

- (void) prepareForSegue:(UIStoryboardSegue*)segue sender:(id)sender
{
    if( [[segue identifier] isEqualToString:@"showLog"] ) {
        UIViewController* logView = segue.destinationViewController;
        if( [logView respondsToSelector:@selector(setManagedObjectContext:)] ) {
            [logView setValue:self.managedObjectContext forKey:@"managedObjectContext"];
        }
    }
}

The Storyboard session from last year’s WWDC is good watching, if you haven’t seen it.