managedObjectContext unrecognized selector sent to instance

Question

I am following a tutorial to develop an iOS app. I am using core data. The first view of the app is RootViewController. All Core Data stack is on the AppDelegate file. This is the part of the code from AppDelegate.m that makes the call to the RootViewController file:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
{
  // Fetch the data to see if we ought to pre-populate
  NSError *error = nil;
  if (![[self fetchedResultsController] performFetch:&error]) {
    NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
    abort();
  }

  [self loadFavoriteThingsData];        

  RootViewController *rootViewController = (RootViewController *)[navigationController topViewController];
  [rootViewController setManagedObjectContext:[self managedObjectContext]];       

  [window addSubview:[navigationController view]];
  [window makeKeyAndVisible];
  return YES;
}

Now, in another part of the app I need to open a new view Controller that is a duplicate of RootViewController, called DoneViewController, but using other NSPredicates to show other core data objects.

In RootViewController there is a button to open the MenuViewController file, from there I try to open DoneViewController using following method:

- (IBAction)doneToDoaction:(id)sender {
    DoneViewController *viewController = [[DoneViewController alloc] init];

    [self presentViewController:viewController animated:YES completion:nil];
}

but an exception is fired:

[MenuViewController managedObjectContext]: unrecognized selector sent to instance 0x145a0c00
2013-12-26 22:58:23.688  *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[MenuViewController managedObjectContext]: unrecognized selector sent to instance

I guess I have to pass the managedObjectContext from RootViewController to MenuViewController and then from MenuViewController to DoneViewController, but I don't know how to do it.

you don't have to pass the managedObjectContext from one viewcontroller to another you can do it eaisly by making a instance of managedObjectContext in appDelegate and use that context where ever you need by simply making the instance of the appDelegate. — Gyanendra

Waqar Ahmed Waqar Ahmed · Accepted Answer · 2015-04-16T13:20:27

This is due to that you are not using NSObject class. For this you have to implement NSObject in you AppDelegate.h.Like this..

@interface AppDelegate : UIResponder <UIApplicationDelegate,NSObject>{
    NSManagedObjectModel *managedObjectModel;
    NSManagedObjectContext *managedObjectContext;
    NSPersistentStoreCoordinator *persistentStoreCoordinator;
}

and also add the properties.

@property (nonatomic, retain, readonly) NSManagedObjectModel *managedObjectModel;
@property (nonatomic, retain, readonly) NSManagedObjectContext *managedObjectContext;
@property (nonatomic, retain, readonly) NSPersistentStoreCoordinator *persistentStoreCoordinator;

- (NSString *)applicationDocumentsDirectory;

Also add code in AppDelegate.m file...

 - (NSManagedObjectContext *) managedObjectContext {
    if (managedObjectContext != nil) {
        return managedObjectContext;
    }
    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil) {
        managedObjectContext = [[NSManagedObjectContext alloc] init];
        [managedObjectContext setPersistentStoreCoordinator: coordinator];
    }

    return managedObjectContext;
}

 - (NSManagedObjectModel *)managedObjectModel {
    if (managedObjectModel != nil) {
        return managedObjectModel;
    }
    managedObjectModel = [NSManagedObjectModel mergedModelFromBundles:nil] ;

    return managedObjectModel;
}

 - (NSPersistentStoreCoordinator *)persistentStoreCoordinator

 {

    if (persistentStoreCoordinator != nil) {
        return persistentStoreCoordinator;
    }
    NSURL *storeUrl = [NSURL fileURLWithPath: [[self  applicationDocumentsDirectory]
                                               stringByAppendingPathComponent: @"<Project Name>.sqlite"]];
    NSError *error = nil;
    persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc]
                                  initWithManagedObjectModel:[self managedObjectModel]];
        if(![persistentStoreCoordinator      addPersistentStoreWithType:NSSQLiteStoreType configuration:nil   URL:storeUrl options:nil error:&error]) 
  {
        /*Error for store creation should be handled in here*/
  }

    return persistentStoreCoordinator;
}
- (NSString *)applicationDocumentsDirectory {
    return [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES) lastObject];
}

This works for me 100%. Hope so that it work for you.

managedObjectContext unrecognized selector sent to instance

2 Answers