Set managedObjectContext of a UITableViewController with a UINavigationController - ios

Question

I have looked at other questions and answers but I still cannot set the managedObjectContext of a UITableViewController embedded in a UINavigationController. Here is my current code:
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
UIStoryboard *sb = [UIStoryboard storyboardWithName:#"Main" bundle:nil];
UINavigationController *navigationController = [sb instantiateViewControllerWithIdentifier:#"Learn"];
MasterViewController *controller = (MasterViewController *)navigationController.topViewController;
controller.managedObjectContext = self.managedObjectContext;
return YES;
}
However when I run the code, the app crashes and produces a log output of this:
+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name
When I try just logging NSLog(#"%#", self.managedObjectContext); in the MasterViewController the result is `(null)
I created my managedObjectContext like so and it received no errors:
- (NSManagedObjectContext *)managedObjectContext {
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
}
return _managedObjectContext;
}
N.B. I am trying to set a UITableViewController that is not the initial view controller
Any ideas? Thanks in advance!

Answer 1

If you are using the boilerplate Apple template (from Xcode), your app delegate should have a method like this, creating the managed objects dynamically when you call self.managedObjectContext:
- (NSManagedObjectContext *)managedObjectContext
{
if (_managedObjectContext != nil) {
return _managedObjectContext;
}
NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
if (coordinator != nil) {
_managedObjectContext = [[NSManagedObjectContext alloc] init];
[_managedObjectContext setPersistentStoreCoordinator:coordinator];
}
return _managedObjectContext;
}
Put a breakpoint there and check that you pass the correct context to the view controller. Make sure the VC property is (nonatomic, strong).

Answer 2

If your navigation controller is set as the initial controller in the storyboard, then the problem is that you're instantiating a new instance of that navigation controller with instantiateViewControllerWithIdentifier. You should get the reference to MasterViewController like this instead:
MasterViewController *controller = (MasterViewController *)[(UINavigationController *)self.window.rootViewController topViewController];