Question

I have specified a NSFetchtedResultsController as property…

@property (nonatomic, strong) NSFetchedResultsController *controller;

… and set the delegate to my class.

self.controller.delegate = self;

Then I have implemented the in the headline mentioned method and put a breakpoint in it.

    - (void)controller:(NSFetchedResultsController *)controller 
                didChangeObject:(id)anObject 
                atIndexPath:(NSIndexPath *)indexPath 
                forChangeType:(NSFetchedResultsChangeType)type 
                newIndexPath:(NSIndexPath *)newIndexPath 
    {    

    => BREAKPOINT <=

    }

I have created the fetch request for the controller as follows:

  NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] initWithEntityName:@"Post"]; 
   // ... some sort ...
    self.controller = [[NSFetchedResultsController alloc]
                       initWithFetchRequest:fetchRequest
                       managedObjectContext:self.context
                       sectionNameKeyPath:nil
                       cacheName:@"cache"];

Now I am storing in another class in the same context some NSManagedObjects of the type “Post” but the didChangeObject method is never called (where my breakpoint is in it).

Does anyone know what is going wrong?

Update #1: The class which fetches some posts from a server and stores it into the context is executed asynchronously using GCD.

Update #2: I have tried it in another way due it does not work to use a context in a multithreaded environment. (Thanks to svena)
Now the ServerConnection runs in an async block (using GCD) and performs a selector on the main thread. This selector method stores the posts in the database and SHOULD update the tableview. Basically, I thought that when I store something in this context the didChangeObject method should be called automatically? But it does not. :-/

I have added a short sequence diagram to illustrate my current status.

Does anyone know why this does not work? Please be patient. I am new to CoreData and Objective-C. 🙂

Answer 1

Update #1: The class which fetches some posts from a server and stores it into the context is executed asynchronously using GCD.

if this is the case, how are you creating your managed object context for the GCD block?
Neither contexts or managed objects are thread safe and cannot be passed around between threads. Furthermore changes made to context on one thread is not automatically propagated to contexts on other threads. Prior to iOS5 that means listening to NSManagedObjectContextDidSaveNotification and merging it there by using mergeChangesFromContextDidSaveNotification: method for your NSFetchedResultsController instance to see it.

Great diagram by the way 🙂

Could you please show the code at the points where you:

1. Create your context
2. Perform your block on the main thread to insert
   data