Question

I am creating an FBChat using XMPP.I have made separate classes for coredata and fetchedResults.

CoreDataClass:

@implementation CoreDataClass

@synthesize managedObjectContext = __managedObjectContext;
@synthesize managedObjectModel = __managedObjectModel;
@synthesize persistentStoreCoordinator = __persistentStoreCoordinator;


- (NSManagedObjectContext *)managedObjectContext
{

    if (__managedObjectContext != nil)
    {
        return __managedObjectContext;
    }

    NSPersistentStoreCoordinator *coordinator = [self persistentStoreCoordinator];
    if (coordinator != nil)
    {
        __managedObjectContext = [[NSManagedObjectContext alloc] init] ;
        [__managedObjectContext setPersistentStoreCoordinator:coordinator];
    }
    return __managedObjectContext;
}


- (NSManagedObjectModel *)managedObjectModel
{
    if (__managedObjectModel != nil)
    {
        return __managedObjectModel;
    }
    NSURL *modelURL = [[NSBundle mainBundle] URLForResource:@"Chat" withExtension:@"momd"];
    __managedObjectModel = [[NSManagedObjectModel alloc] initWithContentsOfURL:modelURL];
    return __managedObjectModel;
}


- (NSPersistentStoreCoordinator *)persistentStoreCoordinator
{
    if (__persistentStoreCoordinator != nil)
    {
        return __persistentStoreCoordinator;
    }
    AppDelegate *delegate = (AppDelegate *)[[UIApplication sharedApplication] delegate];
    NSURL *storeURL = [[delegate applicationDocumentsDirectory] URLByAppendingPathComponent:@"FacebookChat.sqlite"];
    NSError *error = nil;
    __persistentStoreCoordinator = [[NSPersistentStoreCoordinator alloc] initWithManagedObjectModel:[self managedObjectModel]];



    if (![__persistentStoreCoordinator addPersistentStoreWithType:NSSQLiteStoreType configuration:nil URL:storeURL options:nil error:&error])
    {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }    

    return __persistentStoreCoordinator;
}
- (void)saveContext
{
    NSError *error = nil;
    NSManagedObjectContext *managedObjectContext = self.managedObjectContext;
    if (managedObjectContext != nil)
    {
        if ([managedObjectContext hasChanges] && ![managedObjectContext save:&error])
        {
                       NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
            abort();
        } 
    }
}

FetchedControlClass:

@implementation FetchedControllClass
@synthesize fetchedResultsController;

#pragma mark Fetched Results

- (NSFetchedResultsController *)fetchedResultsController
{
    CoreDataClass *coreDataObject=[[CoreDataClass alloc]init];

    if (fetchedResultsController != nil) {
        return fetchedResultsController;
    }


    NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
    NSEntityDescription *entity = [NSEntityDescription entityForName:@"Conversation" inManagedObjectContext:coreDataObject.managedObjectContext];
    [fetchRequest setEntity:entity];
    [fetchRequest setFetchBatchSize:20];
    NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"facebookName" ascending:YES];

    NSArray *sortDescriptors = [NSArray arrayWithObjects:sortDescriptor, nil];    
    [fetchRequest setSortDescriptors:sortDescriptors];
    [sortDescriptor release];

    NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest managedObjectContext:coreDataObject.managedObjectContext sectionNameKeyPath:nil cacheName:@"Master"] ;
    [fetchRequest release];
    aFetchedResultsController.delegate = self;
    self.fetchedResultsController = aFetchedResultsController;
    [aFetchedResultsController release];
    NSError *error = nil;
    if (![self.fetchedResultsController performFetch:&error]) {

        NSLog(@"Unresolved error %@, %@", error, [error userInfo]);
        abort();
    }
    [coreDataObject release];
    return fetchedResultsController;
}    

- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller
{
    AlertListVC *alertListObject=[[AlertListVC alloc]initWithNibName:@"AlertListVC" bundle:nil];

    [alertListObject.tableView beginUpdates];
    [alertListObject release];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo
           atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type
{
    AlertListVC *alertListObject=[[AlertListVC alloc]initWithNibName:@"AlertListVC" bundle:nil];


    switch(type) {
        case NSFetchedResultsChangeInsert:
            [alertListObject.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [alertListObject.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
    [alertListObject release];
}

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath
{
    AlertListVC *alertListObject=[[AlertListVC alloc]initWithNibName:@"AlertListVC" bundle:nil];

    UITableView *tableView = alertListObject.tableView;

    switch(type) {
        case NSFetchedResultsChangeInsert:
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeDelete:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;

        case NSFetchedResultsChangeUpdate:
            [alertListObject configureCell:[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
            break;

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath]withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
    [alertListObject release];
}

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
    AlertListVC *alertListObject=[[AlertListVC alloc]initWithNibName:@"AlertListVC" bundle:nil];
    [alertListObject.tableView endUpdates]; 
    [alertListObject release];

}

I have made objects for both classes in the MainChatClass and adding the conversation from coredata to ConversationClass

Conversation *conversation = (Conversation *)[NSEntityDescription
                                                          insertNewObjectForEntityForName:@"Conversation"
                                                          inManagedObjectContext:coreDataClassObject.managedObjectContext];

I am able to get the fetchedResults but
The issue is:
Coredata methods are getting caleed two times(so file is creating two times).If I am selecting the friend to chat,then the application will crash.I have used zombies for tracking the issue.It is showing some errors as
responsible caller:
1.[MainChatClass tableView:didSelectRowAtIndexPath]
2.[NSFetchedResultsController(Private Methods) _managedObjectContextDidChange]

I have tried many times,but still getting errors with these methods.
If any one having idea for this then please help me.
Thanks in advance

Answer 1

In each of the FRC delegate methods you create a new alertListObject. That makes no sense. You must send the update messages to your existing table view.

The crash occurs because alertListObject.tableView is nil for a newly created view controller.