Question

I need to use core data to persist data for my project, what I have done so far compiles well, but when I actually start storing things using core data, the program just quits, and I don’t know the reason. I set up all the required components for core data in the appDelegate file, and I want to store data in a viewController called DetailViewController. Here is what I have done:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {    

    // Override point for customization after application launch.

    // Set the tab bar controller as the window's root view controller and display.
    self.window.rootViewController = self.tabBarController;
    [self.window makeKeyAndVisible];

//this is what I added, reference managedObjectContext in the detail view controller.

    detailViewController = [[DetailViewController alloc] init];
    detailViewController.managedObjectContext = [self managedObjectContext];

    return YES;
}

All components for core data have been implemented

- (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] retain];

    return managedObjectModel;
}

- (NSPersistentStoreCoordinator *)persistentStoreCoordinator {
    if (persistentStoreCoordinator != nil) {
        return persistentStoreCoordinator;
    }
    NSURL *storeUrl = [NSURL fileURLWithPath: [[self applicationDocumentsDirectory]
                                           stringByAppendingPathComponent: @"MyProjectName.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];
}

When I try to call a method in the detail view to store data, the program quits.

-(IBAction) addItem {
    Info *info = [NSEntityDescription insertNewObjectForEntityForName:@"Info" 
                                                   inManagedObjectContext:managedObjectContext];
    info.name = item.name;
}

item is the current object in the detail view, Info is the model class file. Do I miss something here?

Thanks!

Update:

The error message in the console is:

Terminating app due to uncaught exception ‘NSInternalInconsistencyException’, reason: ‘+entityForName: could not locate an NSManagedObjectModel for entity name ‘Info”

But I do have a Info.xcdatamodel file in the “Resources” folder, and entity name is “Info”.

Answer 1

Did you call [self.managedObjectContext save:&error]?

Also, perhaps your bundle loading routine does not work correctly. Try loading the managedObjectContext like this:

NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"ModelName" 
   withExtension:@"momd"];
__managedObjectModel = [[NSManagedObjectModel alloc] 
   initWithContentsOfURL:modelURL];    
return __managedObjectModel;