NSArrayController and Core Data not behaving as expected

Question

I have a window with a list full of Core Data objects, and a display window that opens when one is selected.

A certain action in the display window marks the Core Data objects as 'Read'.

To open an object, I pass the object to the display window, and also the sortDescriptors and filterPredicate that displayed the list, so the display window can navigate forward/backwards (the main window sometimes displays a subset of objects, which is why I need the sortDescriptors and filterPredicate).

Marking the opened object as read works perfectly. It updates in the main window automatically thanks to KVO.

However, when I navigate forward/back to a different object in the display window, marking as read no longer works. I walk through the code and see the code execute, check the new value, and it is marked as read - but this doesn't reflect in the main window, or in the database.

Is there anything obvious that could be causing this? I am not, at any point, creating a copy of the core data object. The display window uses an NSArrayController to fetch the data, and the sortDescriptors and filterPredicate are applied to it. My code to get the next object looks like this:

-(MyObject *object)nextObject {

    // _object is the object being displayed by the display window.
    // _listContainingObject is an NSArrayController set to Entity: Object

    NSArray *list = [_listContainingObject arrangedObjects];

    NSUInteger positionInList = 0;
    for (MyObject *object in list) {

        if ([[[object objectID] URIRepresentation] isEqualTo: [[_object objectID] URIRepresentation]]) {            break;
        }
        positionInList++;
    }

    if (positionInList == [list count] - 1) return nil;

    if (positionInList + 1 > [list count] - 1) return nil;

    MyObject *object = [list objectAtIndex: positionInList + 1];

    return object;    

}

It really seems like I'm encountering some hidden gotcha of Core Data, like objects pulled out of a different NSArrayController are copies... but everything is running off the same ManagedObjectContext. The NSArrayController's managed object context is bound to a property of my app delegate that returns the same context everything else uses. I am scratching my head pretty hard on this one.

timthetoolman timthetoolman · Accepted Answer · 2011-05-19T17:07:13

remember that when you are working on the items, your managedObjectContext acts as a scratch pad. Your changes to your Managed Objects will not be reflected in the database until you actually save the Managed Object Context.

So after you mark the item as read or unread, you need to save the context.

NSError *saveContextError=nil;
if (![yourManagedObjectContext save:&saveContextError){
    // Handle the error
    NSLog(@"managedObjectContext save error:  %@",error);
}

NSArrayController and Core Data not behaving as expected

1 Answers