Multi-threaded Core Data import example

DDImportOperation.h

@interface DDImportOperation

@property (strong, nonatomic) NSPersistentStoreCoordinator *persistentStoreCoordinator;
@property (strong, nonatomic) NSManagedObjectContext *managedObjectContext;

-(void)initWithPersistentStoreCoordinator:(NSPersistentStoreCoordinator*)persistentStoreCoordinator;
-(void)saveChanges;

@end

DDImportOperation.m

#import "DDImportOperation.h"

@implementation DDImportOperation

@synthesize managedObjectContext=managedObjectContext_,
            persistentStoreCoordinator=persistentStoreCoordinator_;

- (void)initWithPersistentStoreCoordinator:(NSPersistentStoreCoordinator*)persistentStoreCoordinator {
  if (self = [super init]) {
    self.persistentStoreCoordinator = persistentStoreCoordinator;
  }
  return self;
}

- (NSManagedObjectContext*)managedObjectContext {
  if (!managedObjectContext_) {
    managedObjectContext_ = [NSManagedObjectContext new];
    managedObjectContext_.persistentStoreCoordinator = self.persistentStoreCoordinator;
  }
  return managedObjectContext_;
}

- (void)main {
  // Do work, then
  [self saveChanges];
}

- (void)saveChanges {
  if ([[self threadedContext] hasChanges]) {
    NSError *error;
    BOOL contextDidSave = [[self threadedContext] save:&error];
    if (!contextDidSave) {
      // TODO: Handle error in a nicer way than:
      abort()
    }
  }
}

@end

DDItemListViewController.m

@implementation DDItemListViewController

// This object has pointers to a persistent store coordinator (self.psc) and
// MOC (self.managedObjectContext). For the sake of example, let's say this
// controller presents a UITableView backed by an NSFetchedResultsController,
// which in turn gets its data from self.managedObjectContext.
// In theory, when changes are merged into this controller's MOC the UI
// should be updated

// This is just for purposes of illustration; in the real app, imports/syncs
// could also be triggered by a timer, or on app launch, or whenever a local
// object is saved
-(IBAction)startImport {
  NSOperationQueue *dataQueue = [[[UIApplication sharedApplication] delegate] dataQueue];
  DDImportOperation *importOperation = [[DDImportOperation alloc] initWithPersistentStoreCoordinator:self.psc];

  [[NSNotificationCenter defaultCenter] addObserver:self
                                        selector:@selector(mergeChangesFromImport:)
                                        name:NSManagedObjectContextDidSaveNotification
                                        object:importOperation.managedObjectContext];

  [dataQueue addOperation:importOperation];
}

-(void)mergeChangesFromImport:(NSNotification*)notification {
  SEL selector = @selector(mergeChangesFromContextDidSaveNotification:);

  [self.managedObjectContext performSelectorOnMainThread:selector
                             withObject:notification
                             waitUntilDone:YES];

  // TODO: Need to remove myself as an observer on importOperation's managed object context
  // but also need to retain a reference to it somewhere?
  // [[NSNotificationCenter defaultCenter] removeObserver:self
  //                                       name:NSManagedObjectContextDidSaveNotification
  //                                       object:[self threadedContext]];
}


@end