How to "listen" for changes to a specific object with simperium

Question

I wonder if you can help me to understand how to make this code "listen" to changes from simperium. When using NSFetchedResultsController it all happens automatically, but how would I do with the following code? Tried to read the document but it was not really clear to me.

NSError *error;
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
fetchRequest.entity = [NSEntityDescription entityForName:kPersonEntity inManagedObjectContext:self.managedObjectContext];

NSPredicate *predicate = [NSPredicate predicateWithFormat:@"title == queen"];
NSArray *array = [[self.managedObjectContext executeFetchRequest:fetchRequest error:&error] filteredArrayUsingPredicate:predicate];

if(array.count > 0) {
    _queen = (Person *)[array objectAtIndex:0];
}

Thanks!

Answer 1

You can listen to NSManagedObjectContextDidSaveNotification notifications and act accordingly. Once Simperium processes and saves any changes, you'll receive a NSManagedObjectContextDidSaveNotification notification. Listen for it:

[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(contextSaved:) name:NSManagedObjectContextDidSaveNotification object:ctx];

Then, in your contextSaved: method, you filter out the objects you care about

    - (void)contextSaved:(NSNotification *)n
    {
        NSDictionary *userInfo = [n userInfo];
        NSSet *objects = <see NSManagedObjectContext Change Notification User Info Keys>
        <filter/process objects>
    }

Also, don't forget to removeObserver:

[[NSNotificationCenter defaultCenter] removeObserver:self];