iOS CoreData无法使用Objective-C获取属性

Question

I try to using objective-c write the core data.

My swift code can get the User Entites like below

swift3:

 let appDel = UIApplication.shared.delegate as? AppDelegate;
 guard let context = appDel?.persistentContainer.viewContext else{ return }
 let User = User(context: context);

I using objective-c write in the viewdidload.

But I can't persistentContainer property.

like below:

Objective-c

  UIApplication *application = [UIApplication sharedApplication];

  NSManagedObjectContext *context = (AppDelegate*)(application.delegate).
                                     persistentContainer.viewContext;

Have anyone can resolve the problem about can't get persistentContainer property?

I using the Xcode8.2.1 objective-c project.

Thank you very much.

Answer 1

*First we should import core data framework in Appdelegate and set the property of persistentContainer In Appdelegate.h file

@property (readonly, strong) NSPersistentContainer *persistentContainer;

- (void)saveContext;

In Appdelegate.m file

@synthesize persistentContainer = _persistentContainer;

- (NSPersistentContainer *)persistentContainer {
    // The persistent container for the application. This implementation creates and returns a container, having loaded the store for the application to it.
    @synchronized (self) {
        if (_persistentContainer == nil) {
            _persistentContainer = [[NSPersistentContainer alloc] initWithName:@"NSURL"];
            [_persistentContainer loadPersistentStoresWithCompletionHandler:^(NSPersistentStoreDescription *storeDescription, NSError *error) {
                if (error != nil) {
                    // 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.

                    /*
                     Typical reasons for an error here include:
                     * The parent directory does not exist, cannot be created, or disallows writing.
                     * The persistent store is not accessible, due to permissions or data protection when the device is locked.
                     * The device is out of space.
                     * The store could not be migrated to the current model version.
                     Check the error message to determine what the actual problem was.
                    */
                    NSLog(@"Unresolved error %@, %@", error, error.userInfo);
                    abort();
                }
            }];
        }
    }

    return _persistentContainer;
}

#pragma mark - Core Data Saving support

- (void)saveContext {
    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();
    } 
}