Question

I have several NSFetchedResultsControllers throughout my app, and in every view controller, I implement the respective delegate methods. However, instead of copying these delegate methods into every class that implements an NSFetchedResultsController, I thought I would just create a class that implements these delegate methods, and set all fetched results controller’s delegate to point to that one class. Here’s what I’ve tried, which doesn’t work:

Since the delegate methods need to know which table view they are making changes to, I thought I would just create a separate delegate class for each fetched results controller, and send a pointer to the tableview for that class:

FetchedResultsDelegate *delegate = [[FetchedResultsDelegate alloc] initWithTableView:parentTableView];
self.fetchedResultsController.delegate=delegate;
[delegate release];

However, this causes a BAD_ACCESS crash, so this means that I probably shouldn’t be doing what I’m doing above.

How can I create a single delegate class that handles all delegate requests for all my NSFetchedResultsControllers?

Edit: I was able to fix the problem by doing @property (nonatomic, retain) FetchedResultsDelegate *delegate; Is this ok? Some people are saying something about assign rather than retain?

Answer 1

Nothing is retaining your FetchedResultsDelegate as delegate properties are normally declared as assign. e.g. NSFetchedResultsController declares the delegate as

@property(nonatomic, assign) id <NSFetchedResultsControllerDelegate> delegate

Therefore you created the object and destroyed it straight away, but gave the fetchedResultsController a nasty dangling pointer.

To fix this you need a retain on the delegate. So in your UITableViewController class add a new property

// .h
@property (nonatomic, strong) id<NSFetchedResultsControllerDelegate> tableViewDelegate;

// .m
@synthesize tableViewDelegate = _tableViewDelegate;

then when you hook up you delegate just change your code to this

FetchedResultsDelegate *delegate = [[FetchedResultsDelegate alloc] initWithTableView:parentTableView];
self.fetchedResultsController.delegate = delegate;
self.tableViewDelegate = delegate;
[delegate release]; delegate = nil;

Don’t forget

Release this new ivar in the dealloc

- (void)dealloc;
{
    // ... other releases
    [_tableViewDelegate release];
    [super dealloc];
}

---

The use of assign is all about ownership semantics.

In this case your UITableViewController should own the tableView’s delegate (e.g. strong/retain) as nothing else is.

The reason that the NSFetchedResultsController uses assign and not retain/strong is because there is a good chance that the object that created it would act as the delegate, which would result in both objects owning each other (both having a retain held on each other), which causes a retain cycle