An NSManagedObject of class 'NSManagedObject' must have a valid NSEntityDescription

Question

I am working on Objective-C with CoreData, i am getting below error...

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'An NSManagedObject of class 'NSManagedObject' must have a valid NSEntityDescription.'

I added CoreData to my project. I created saveData method in viewControllerA and i called it in viewControllerB.

In this scenario I am getting error, if I call saveData method in viewDidLoad of viewControllerA it's working properly.

In AppDelegate.h

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

In AppDelegate.m

#pragma mark - Core Data stack

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

- (NSURL *)applicationDocumentsDirectory {
// The directory the application uses to store the Core Data store file. This code uses a directory named "com.brninfotech._607_introToCoreDataFinal" in the application's documents directory.
return [[[NSFileManager defaultManager] URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask] lastObject];
}

- (NSManagedObjectModel *)managedObjectModel {
// The managed object model for the application. It is a fatal error for the application not to be able to find and load its model.
if (_managedObjectModel != nil) {
    return _managedObjectModel;
}
NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"VehicleNumberDataBase" withExtension:@"momd"];
_managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
return _managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
// The persistent store coordinator for the application. This implementation creates and returns a coordinator, having added the store for the application to it.
if (_persistentStoreCoordinator != nil) {
    return _persistentStoreCoordinator;
}

// Create the coordinator and store

_persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];
NSURL *storeURL = [[self applicationDocumentsDirectory] URLByAppendingPathComponent:@"VehicleNumberDataBase.sqlite"];


//    NSLog(@"StoreURL is %@",storeURL);
NSError *error = nil;
NSString *failureReason = @"There was an error creating or loading the application's saved data.";
if (![_persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error]) {
    // Report any error we got.
    NSMutableDictionary *dict = [NSMutableDictionary dictionary];
    dict[NSLocalizedDescriptionKey] = @"Failed to initialize the application's saved data";
    dict[NSLocalizedFailureReasonErrorKey] = failureReason;
    dict[NSUnderlyingErrorKey] = error;
    error = [NSError errorWithDomain:@"YOUR_ERROR_DOMAIN" code:9999 userInfo:dict];
    // Replace this 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();
}

return _persistentStoreCoordinator;
}


- (NSManagedObjectContext *)managedObjectContext {
// Returns the managed object context for the application (which is already bound to the persistent store coordinator for the application.)
if (_managedObjectContext != nil) {
    return _managedObjectContext;
}

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

#pragma mark - Core Data Saving support

- (void)saveContext {
NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
if (managedObjectContext != nil) {
    NSError *error = nil;
    if ([managedObjectContext hasChanges] && ![managedObjectContext 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();
    }
}
}


in viewControllerA viewDidLoad 

self.ad = (AppDelegate *)[[UIApplication sharedApplication]delegate];
self.VehicleNumberED = [NSEntityDescription entityForName:@"VehicleNumberEntity" inManagedObjectContext:self.ad.managedObjectContext];

- (void)saveData {

NSManagedObject * managedObj = [[NSManagedObject alloc]initWithEntity:self.VehicleNumberED insertIntoManagedObjectContext:self.ad.managedObjectContext];

[managedObj setValue:self.textFieldString forKey:@"vehicleNumberAtt"];

NSError * errorObj;
[self.ad.managedObjectContext save:&errorObj];

if (errorObj) {
    NSLog(@"Something goes wrong");
}else {
    NSLog(@"Saved Successfully");
}

NSFetchRequest * fetReq = [NSFetchRequest fetchRequestWithEntityName:@"VehicleNumberEntity"];

NSError * fetchErrorObj;

self.storedDataArray = [self.ad.managedObjectContext executeFetchRequest:fetReq error:&fetchErrorObj];


NSLog(@"array count is %lu", self.storedDataArray.count);

for (int i=0; i<self.storedDataArray.count; i++) {

    self.storedManagedObj = [self.storedDataArray objectAtIndex:i];

    self.vehicleNumberArray = [self.storedManagedObj valueForKey:@"vehicleNumberAtt"];

}

NSLog(@"Vehicle number is : %@", [self.storedManagedObj valueForKey:@"vehicleNumberAtt"]);

}

in ViewVontrollerB 

- (IBAction)saveVehicleNumberButton:(UIButton *)sender {

VehicleDetailsViewController *vedvc = [[VehicleDetailsViewController alloc]init];
vedvc = [self.storyboard instantiateViewControllerWithIdentifier:@"VeDVC"];
vedvc.textFieldString = self.vehicleNumberTextField.text;
[vedvc saveData];

[self.navigationController pushViewController:vedvc animated:YES];
}

Answer 1

The issue here is that you are executing [vedvc saveData] before displaying the vedvc view controller. At this point, vedvc has not been displayed, so its viewDidLoad has not yet been executed. Consequently self.ad and self.VehicleNumberED are both nil. Hence the error: the entity description is nil.

The simplest fix would be to move the initialisation of those two variables (ad and VehicleNumberED) to the saveData method. But you might do better to rethink your code structure.