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:
- (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:
- (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;
}