Core Data error: nil is not a legal NSManagedObjectContext parameter

Question

I'm entirly new to creating iOS apps. I have to quickly create a form-application where I can store information from people willing to fill it in. Basicly just a bunch of text-fields for stuff like name, mail etc.

Once the form is filled, I'm storing their data with this bit of code:

//Save action
NSEntityDescription *entityDesc = [NSEntityDescription entityForName:@"Person" inManagedObjectContext: context];
NSManagedObject *newPerson = [[NSManagedObject alloc]initWithEntity:entityDesc insertIntoManagedObjectContext:context];

//Fill in values
[newPerson setValue:self.btnPrefix.titleLabel.text forKey: @"prefix"];
[newPerson setValue:self.txtFirstName.text forKey: @"firstname"];
[newPerson setValue:self.txtLastName.text forKey: @"lastname"];
[newPerson setValue:self.txtLive.text forKey: @"country"];
[newPerson setValue:self.txtMail.text forKey: @"email"];
[newPerson setValue:self.txtPhone.text forKey: @"phonenumber"];
[newPerson setValue:self.txtLinked.text forKey: @"linkedIn"];
[newPerson setValue:self.txtAbout.text forKey: @"about"];

NSError *error;
[context save:&error];

When executed on the simulator no problem at all. But once ran on the iPad I get this error:

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '+entityForName: nil is not a legal NSManagedObjectContext parameter searching for entity name 'Person''

After debugging it gets triggerd on the first line:

NSEntityDescription *entityDesc = [NSEntityDescription entityForName:@"Person" inManagedObjectContext: context];

After a bit more research, my Appdelegate contains a nil persistentContainer when ran on device, but it's filled when ran on virtual device. So I guess the problem is there, but I can't find a way to solve it.

- (void)viewDidLoad {
    [super viewDidLoad];
    AppDelegate *appdelegate = (AppDelegate*)[[UIApplication sharedApplication]delegate];
    context = appdelegate.persistentContainer.viewContext;
}

Can anyone help me out?

The error tells you that your context parameter is nil, which must not be the case. How do you get the managed object context object you're passing in there? And I assume you have ensured that your model does contain an Entity with the name "Person", right? — Gero
under viewDidLoad AppDelegate *appdelegate = (AppDelegate*)[[UIApplication sharedApplication]delegate]; context = appdelegate.persistentContainer.viewContext;. And yes I have a model that contains the entity Person. As I said it works on the simulator so I imagine there's just a thing missing to make it work on a physical device? — Akorna
After a bit more research, my Appdelegate contains a nil persistentContainer when ran on device, but it's filled when ran on virtual device. So I guess the problem is there, but I can't find a way to solve it. — Akorna
I assume you're just using a standard template for core data. So why not look into the persistentContainer method your app delegate has by default? It sounds like you're either trying to initiate a container in a location you don't have write access to on the device (the simulator usually has more write permissions in various places) or you're facing a racing condition on device (your view controller tries to access the container and context before the loadPersistentStoresWithCompletionHandler: method is done). — Gero
No problem, it just seemed to me it was a bit "early" to ask, but I realize what is "too early" and what not depends on the individual and you did say you were new. I am glad you found the root of this, I guess now you can see this would have been hard to figure out for anybody who hasn't your project right in front of them AND has had a similar experience. I wanted to prevent that you might come to the conclusion people on SO are "above" helping a new coder. :) Again, I am glad you figured it out on your own. — Gero

Akorna Akorna · Accepted Answer · 2017-05-19T09:50:36

For those encountering this error. Most probably if it works on the virtual device but not on the physical device it's due to the differences for accessing core data between iOS 9 and 10.

In Xcode 8 the AppDelegate automaticly generates data for iOS 10 but if you're stuck on iOS 9 you'll need to add the following code in your delegate file:

@synthesize managedObjectContext = _managedObjectContext;
@synthesize managedObjectModel = _managedObjectModel;
@synthesize persistentStoreCoordinator = _persistentStoreCoordinator;

- (NSURL *) applicationDocumentsDirectory{
    return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

- (NSManagedObjectModel *)managedObjectModel {
    if(_managedObjectModel != nil){
        return _managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"StylelabsForms" withExtension:@"momd"];
    _managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return _managedObjectModel;
}

- (NSPersistentStoreCoordinator *) persistentStoreCoordinator{
    if(_persistentStoreCoordinator != nil){
        return _persistentStoreCoordinator;
    }

    _persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
    NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"StylelabsForms.sqlite"];
    NSError *error = nil;
    NSString *failureReason = @"Error loading saved data";
    if(![_persistentStoreCoordinator addPersistentStoreWithType: NSSQLiteStoreType configuration:nil URL: storeURL options:nil error:&error]){
        NSMutableDictionary *dict = [NSMutableDictionary dictionary];
        dict[NSLocalizedDescriptionKey] = @"Failed init application's saved data";
        dict[NSLocalizedFailureReasonErrorKey] = failureReason;
        dict[NSUnderlyingErrorKey] = error;
        error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }

    return _persistentStoreCoordinator;
}

- (NSManagedObjectContext *) managedObjectContext {
    if (_managedObjectContext != nil){
        return _managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if(!coordinator) {
        return nil;
    }
    _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType];
    [_managedObjectContext setPersistentStoreCoordinator:coordinator];

    return _managedObjectContext;
}

Also adapt the save as followed:

- (void)saveContext {
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if(managedObjectContext != nil){
        NSError *error = nil;
        if([managedObjectContext hasChanges] && ![managedObjectContext save:&error]){
            NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        }
    }

    //For iOS 10 and above
    /*
    NSManagedObjectContext *context = self.persistentContainer.viewContext;
    NSError *error = nil;
    if ([context hasChanges] && ![context save:&error]) {
        // Replace this implementation with code to handle the error appropriately.
        // abort() causes the application to generate a crash log and terminate. You should not use this function in a shipping application, although it may be useful during development.
        NSLog(@"Unresolved error %@, %@", error, error.userInfo);
        abort();
    } */
}

Core Data error: nil is not a legal NSManagedObjectContext parameter

2 Answers