Can't Release NSFetchedResultsController in dealloc

Question

I have two UITableViewControllers with a fairly simple ui flow. One UITableViewController loads another UITableViewController when you select an item in the first UITableViewController.

---

(UITableViewController) List of Stories -> Select a Story -> (UITableViewController) List of Sentences

---

In the second UITableViewController (MakeSentenceDetailViewController) I can't release my NSFetchedResultsController without causing an error (shown with Zombies set to on):

-[NSFetchRequest release]: message sent to deallocated instance 0x5b370f0

The retain count of the NSFetchedResultsController stays at 1 but when I try to release it in dealloc I get a crash.

The code, especially in regards to the NSFetchedResultsController is the same in both tableviews, but in the MakeSentenceDetailViewController I can't release this NSFetchedResults Controller with a crash - giving me a leak.

How can I safely release my NSFetchedResultsController? Why does it work fine in the parent (first) tableviewcontroller - but not in the second?

I can provide code for the first UITableViewController but in regards to NSFetchedResultsController it's declared and used in much the same way.

MakeSentenceTableViewController.h:

@interface MakeSentenceTableViewController : UITableViewController {
NSManagedObjectContext  *managedObjectContext;  
NSFetchedResultsController *fetchedResultsController;
}
@property (nonatomic, retain)  Story *story;
@property (nonatomic, retain) NSManagedObjectContext *managedObjectContext;
@end

MakeSentenceTableViewController.m (relevant code with NSFetchedResultsController):

 - (void)viewDidLoad {
 [super viewDidLoad];
 if (managedObjectContext == nil) 
 { 
 managedObjectContext = [(MyAppAppDelegate *)[[UIApplication sharedApplication] delegate] managedObjectContext];
 NSLog(@"After managedObjectContext: %@",  managedObjectContext);
 }
   NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
  NSEntityDescription *entity = [NSEntityDescription entityForName:@"Sentence" inManagedObjectContext:managedObjectContext];
  [request setEntity:entity];
  //sorting stuff:
  NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"order" ascending: YES];
  NSArray *sortDescriptors = [[NSArray alloc] initWithObjects: sortDescriptor, nil];
  [request setSortDescriptors:sortDescriptors];
  //[request setFetchBatchSize:FETCH_BATCH_SIZE];
  [sortDescriptors release];
  [sortDescriptor release];
  fetchedResultsController = [[NSFetchedResultsController alloc] 
    initWithFetchRequest:request managedObjectContext:managedObjectContext 
    sectionNameKeyPath:nil cacheName:nil];
  [request release];
  NSError *error;
  [fetchedResultsController performFetch:&error];
  NSLog(@"FetchedResultsController: %@", fetchedResultsController);
  NSLog(@"fetchedResultsController RetainCount at viewDidLoad: %d", [fetchedResultsController retainCount]);
 }

 - (void)dealloc {

  //Gotta figure out why I can't release this:
  [fetchedResultsController release]; //Crash! Burn! 
  NSLog(@"fetchedResultsController RetainCount at dealloc: %d", [fetchedResultsController retainCount]);
  [managedObjectContext release];
  [super dealloc];
 }

Answer 1

NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];
// ...snip...
[request release];

You're releasing an object that you've relinquished ownership of (with -autorelease). You don't get an error at the point of the other release because the NSFetchedResultsController is also retaining the fetch request; thus the controller is the one actually causing the crash when it releases the last reference to the fetch request.

Answer 2

You are over-releasing the NSFetchRequest

You autorelease it here:

   NSFetchRequest *request = [[[NSFetchRequest alloc] init] autorelease];

then release it again later:

  [request release];

then later when you release the fetchedResultsController, it tries to release that same request again.