Core Data and threads / Grand Central Dispatch

Question

I'm a beginner with Grand Central Dispatch (GCD) and Core Data, and I need your help to use Core Data with CGD, so that the UI is not locked while I add 40.000 records to Core Data.

I know that CD is not thread safe, so I have to use another context, and then save the data and merge contexts, as far as I was able to understand from some articles.

What I couldn't do yet, is put the pieces together.

So, in my code, I need your help on how to to that.

I have:

/*some other code*/  for (NSDictionary *memberData in arrayWithResult) {      //get the Activities for this member     NSArray *arrayWithMemberActivities = [activitiesDict objectForKey:[memberData objectForKey:@"MemberID"]];      //create the Member, with the NSSet of Activities     [Members createMemberWithDataFromServer:memberData                          andActivitiesArray:arrayWithMemberActivities                               andStaffArray:nil                            andContactsArray:nil                      inManagedObjectContext:self.managedObjectContext]; } 

How can I transform this to work on the background, and then, when done saving, save the data and update the UI, without blocking the UI while saving the 40.000 objects?

Answer 1

Here's a good example for you to try. Feel free to come back if you have any questions:

self.mainThreadContext... // This is a reference to your main thread context NSPersistentStoreCoordinator *mainThreadContextStoreCoordinator = [self.mainThreadContext persistentStoreCoordinator]; dispatch_queue_t request_queue = dispatch_queue_create("com.yourapp.DescriptionOfMethod", NULL); dispatch_async(request_queue, ^{      // Create a new managed object context     // Set its persistent store coordinator     NSManagedObjectContext *newMoc = [[NSManagedObjectContext alloc] init];     [newMoc setPersistentStoreCoordinator:mainThreadContextStoreCoordinator]];      // Register for context save changes notification     NSNotificationCenter *notify = [NSNotificationCenter defaultCenter];     [notify addObserver:self                 selector:@selector(mergeChanges:)                     name:NSManagedObjectContextDidSaveNotification                   object:newMoc];      // Do the work     // Your method here     // Call save on context (this will send a save notification and call the method below)     BOOL success = [newMoc save:&error];     if (!success)         // Deal with error     [newMoc release]; }); dispatch_release(request_queue); 

And in response to the context save notification:

- (void)mergeChanges:(NSNotification*)notification  {     dispatch_async(dispatch_get_main_queue(), ^{         [self.mainThreadContext mergeChangesFromContextDidSaveNotification:notification waitUntilDone:YES];     }); } 

And don't forget to remove the observer from the notification center once you are done with the background thread context.

[[NSNotificationCenter defaultCenter] removeObserver:self];