How to setup NSArrayController with Core Data?

Question

I am trying to programmatically setup an NSArrayController to work with Core Data.

I know that my Core Data store has content since I can manually retrieve objects through the managed object context. I hooked up an NSArrayController to the same managed object context and then bound the value parameter of a NSTableColumn to the NSArrayController.

I asked the NSArrayController to fetch but it returns an empty array.

Any suggestions on what I might be doing wrong?

Interface

@interface MTTableViewController : NSObject <NSTableViewDelegate, NSTableViewDataSource>
{
    NSMutableArray *tableData;
    MTTableCell *tableCell;        

    IBOutlet NSTableColumn *tableColumn;        
    NSArrayController *dataController;
}

Implementation

- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil
{
    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];

    if (self)
    {
        dataController = [[NSArrayController alloc] init];
        [dataController setManagedObjectContext:[[NSApp delegate] managedObjectContext]];
        [dataController setEntityName:@"Track"];
        [dataController setAutomaticallyPreparesContent:YES];

        [dataController fetch:self];
        NSArray *content = [dataController arrangedObjects];        
        NSLog(@"Count :%i", (int)[content count]); //Outputs 0

        tableCell = [[MTTableCell alloc] initTextCell:@""];
        [tableColumn setDataCell:tableCell];
    }

    return self;
}

Answer 1

The fetch: doesn't wait for data to be loaded, instead it returns instantly.

This makes sense in bindings-enabled environment. You usually have a table view bound to an array controller, which updates whenever controller content changes.

In this case you could observe for changes in arrangedObjects of the controller:

[self.arrayController addObserver:self forKeyPath:@"arrangedObjects" options:NSKeyValueObservingOptionNew context:NULL];

And then:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
  NSLog(@"Data: %@", self.arrayController.arrangedObjects);
}

Source: https://stackoverflow.com/a/13389460