Objective C view controller property not saving - ios

Question

Hi I am trying to set my UIViewController's managed object context, but the object context is not saved. Here's the code:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
UIStoryboard *mainStoryboard = [UIStoryboard storyboardWithName:#"Main" bundle: nil];
my_TableViewController *viewController = [mainStoryboard instantiateViewControllerWithIdentifier:#"coretut"];
if ([viewController isKindOfClass:[my_TableViewController class]]) {
[viewController setOManagedObjectContext:self.managedObjectContext];
}
NSLog(#"%#", self.managedObjectContext);
NSLog(#"%#", viewController.oManagedObjectContext);
}
The output for the following is
Apple_Tutorial[11241:461826] <NSManagedObjectContext: 0x7fb558d86600>
Apple_Tutorial[11241:461826] <NSManagedObjectContext: 0x7fb558d86600>
However when i call
NSLog(#"%#", self.oManagedObjectContext);
In viewDidLoad() for my_TableViewController the output is null. oManagedObjectContext is declared as (strong, nonatomic). Does anyone know why oManagedObjectContext went to null?
viewDidLoad code:
- (void)viewDidLoad {
[super viewDidLoad];
UINib *nib = [UINib nibWithNibName:#"my_TableViewCell" bundle:nil];
[[self tableView] registerNib:nib forCellReuseIdentifier:#"tableViewCell"];
NSLog(#"%#", self.oManagedObjectContext);
}

Answer 1

The problem is that didFinishLaunchingWithOptions is instantiating a new view controller and then doing nothing with it (i.e. discarding it). So you're looking at two different view controller instances.
You might have the app delegate set the root view controller's oManagedObjectContext:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
ViewController *controller = (id)self.window.rootViewController;
NSAssert([controller isKindOfClass:[ViewController class]], #"Root controller should be `ViewController`, but is %#", controller);
controller.oManagedObjectContext = self.managedObjectContext;
return YES;
}
Clearly, if your view controller in question isn't the root controller (e.g. if it's in some container view controller, such as navigation controller, tab bar controller, custom container controller, etc.) then you'd have to tweak the above code to navigate through that hierarchy to find your view controller class.