Insert/Modify NSManagedObject with ArrayController and TableView

Question

My app uses Core Data with a simple model with two entities, 'Category' and 'Item', both with a 'name' attribute and a relationship one-to many (a category has many items).

In IB I have a tableview and a Array Controller for the items. Also a textfield and a comboBox (for user type items name and select a category) and "add" button.

What I want is add a new item and modify it with the user´s item name and category selection.

I have tried this:

- (IBAction)add:sender
{
    NSManagedObjectContext *moc = [self managedObjectContext];
    NSEntityDescription *itemEntityDescription = [NSEntityDescription entityForName:@"Item" inManagedObjectContext:moc];

    NSManagedObject *newItem = [[NSManagedObject alloc] initWithEntity: itemEntityDescription insertIntoManagedObjectContext:moc];

    //Modify attribute
    [newItem setValue:[textField stringValue] forKey:@"name"];

    //Setup category relacionship from user selection on comboBox
    NSEntityDescription *categoryEntity = [NSEntityDescription entityForName:@"Category" inManagedObjectContext:moc];
    NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(name LIKE[c] %@)",[comboBox objectValueOfSelectedItem]];

    NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
    [request setEntity:categoryEntity];
    [request setPredicate:predicate];

    NSError *error = nil;
    NSArray *array = [moc executeFetchRequest:request error:&error];

    [newItem setValue:[array objectAtIndex:0] forKey:@"category"];
}

The problem is the new item is not selected in the TableView. And if I use instead [itemsArrayController add:nil]; I can´t access to the new item to modify it.

Any solution? Thanks in advance.

Answer 1

The problem is the array controller has not had time to fetch its new content based on your MOC changes. This typically happens in a future (possibly the very next) trip through the run loop as a result of observing the MOC for changes.

If you want to work with a newly-inserted object in an array controller's selection, you'll have to force the array controller to refresh its content. To do this, just send the array controller a -fetch: after you're done with your manipulations, then the newly-inserted object should be present. You can then modify the array controller's selection directly.