Question

I have an instance of a NSObject class that is supposed to parse a XML and save NSManagedObjects, it does everything ok. But I need to receive a NSManagedObjectContextDidSaveNotification inside it to merge CoreData contexts.

The thing is that my instance is being deallocated sooner then I receive the notification above.

How can I prevent my instance being deallocated sooner?

Here’s when I call my instance

// in my ViewController implementation

WSNoticia *wsNoticia = [WSNoticia new]; // __strong by default right?

Here’s the implementation of WSNoticia:

- (id)init {
    self = [super init];
    if (self) {
        [self parseNews];
    }
    return self;
}

- (void)dealloc {
    // called before mergeChanges: or updateContext:
}

#pragma mark - Private Methods

- (void)parseNews {
    // save context in another thread
    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];

    NSManagedObjectContext *context = [[NSManagedObjectContext alloc] init];
    [context setUndoManager:nil]; // performance benefit
    [context setPersistentStoreCoordinator:[appDelegate persistentStoreCoordinator]];
    [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(mergeChanges:) name:NSManagedObjectContextDidSaveNotification object:context];

    NSBlockOperation *blockOperation = [NSBlockOperation blockOperationWithBlock:^{
     // fetching things
    }];

    [blockOperation setCompletionBlock:^{
        // updating and saving things
        // here the NSManagedObjectContextDidSaveNotification is called (by doing [context save:nil];
    }];

    // add operation to queue
    NSOperationQueue *operationQueue = [NSOperationQueue new];
    [operationQueue addOperation:blockOperation];    
}

// doesn't get called
- (void)updateContext:(NSNotification *)notification {
    NSManagedObjectContext *mainContext = [self managedObjectContext];
    [mainContext mergeChangesFromContextDidSaveNotification:notification];

    [[NSNotificationCenter defaultCenter] postNotificationName:kNotificationNameNoticiasParsed object:self];
}

#pragma mark - NSNotificationCenter

// doesn't get called
- (void)mergeChanges:(NSNotification *)notification {
    [[NSNotificationCenter defaultCenter] removeObserver:self];

    AppDelegate *appDelegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSManagedObjectContext *mainContext = [appDelegate managedObjectContext];
    if ([notification object] == mainContext) {
        // main context save, no need to perform the merge
        return;
    }
    [self performSelectorOnMainThread:@selector(updateContext:) withObject:notification waitUntilDone:YES];
}

Answer 1

The strong lifetime qualifier is applied by default, but the lifetime of your variable is just for the method in which you declare it.

If you declare wsNoticia as an instance variable, you should be fine.