Core Data - sharing NSManagedObjects among multiple threads

Question

I suffered all the consequences of using a single MOC in multiple threads - my app crashes at random points because the MOC is created in the main thread and I also use it t

Answer 1

Use one NSManagedObjectContext per thread. If you communicate between threads, pass the NSManagedObjectID, which is thread safe, and fetch the object again from you thread context. In my apps I sometimes even use one context per controller.

To manage the different contexts, register an Observer for the NSManagedObjectContextDidChangeNotification. Within this notification handling, you pass the notification to each of your contexts via the mergeChangesFromContextDidSaveNotification: method. This method is thread save and makes the context update its state.

After this you have to refresh your views. If you have a table view based application, have a look at NSFetchedResultsController. This helps you update the table automatically with appropriate animations. If you don't use table views, you have to implement the UI update yourself.

Answer 2

If you are only supporting iOS 5 and above you don't need to deal with NSManagedObjectID and merging contexts anymore. You can use the new concurrency types of NSManagedObjectContext instead. Then do your operations within managedObjectContext:performBlock and they will be merged automatically.

See the answer from svena here for more information: Core Data and Concurrency using NSOperationQueues