Prior to iOS 9, Apple would do the heavy lifting and setup a Core Data stack with certain templates. One of those methods was the custom initialiser for the managed object context in the AppDelegate.m file.
Since iOS 9 however, the standard init method is deprecated and we need to use a designated initialiser instead, called initWithConcurrency. This initialiser has been around since iOS 5, but up until now it was optional to use it.
Here’s what a typical custom initialiser for a managed object context looked like prior to iOS 9:
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- (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] init]; [_managedObjectContext setPersistentStoreCoordinator:coordinator]; return _managedObjectContext; } |
Opening a project with a method like this now will give us a deprecation warning and we must use initWithConcurrency instead.
This means that we now have to make a choice about what thread our managed object context is initialised on: the main queue, or perhaps a special background queue we’ve created. Our choices are:
- NSPrivateQueueConcurrencyType
- NSMainQueueConcurrencyType
Unless you have a private queue, the previous default behaviour can be brought back with the latter option. Here’s what the updated method would look like:
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- (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; } // since iOS 9 _managedObjectContext = [[NSManagedObjectContext alloc] initWithConcurrencyType:NSMainQueueConcurrencyType]; [_managedObjectContext setPersistentStoreCoordinator:coordinator]; return _managedObjectContext; } |