One delegate class for multiple NSFetchedResultsController? - iphone

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