NSFetchedResultsControllerDelegate and deleteRowsAtIndexPaths: Section issue - objective-c

Question

In response of a delete operation on a CELL (not a section) of a tableView connected to a NSFetchedResultsController i obtain this error :
'Invalid update: invalid number of
sections. The number of sections
contained in the table view after the
update (1) must be equal to the number
of sections contained in the table
view before the update (2), plus or
minus the number of sections inserted
or deleted (0 inserted, 0 deleted).'
I understand that the problem is related to Section numbers after and before update. It says that i didn't delete sections, but the after-value is different from the before-value.
Ok this's true! but my section depend on row cells, so if i remove the last row cell of a section, the section disappear.
Here how i define Section and Row numbers:
Sections are created to group row by an attribute "date". Thus, if a row has the attribute "date" 10 April 2010 and a second row has 11 April 2010 i have 2 sections containing 1 row.
- (NSInteger)numberOfSectionsInTableView:(UITableView *)tableView {
return [[self.controller sections]count];
}
- (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section {
id <NSFetchedResultsSectionInfo> sectionInfo = [[self.controller sections] objectAtIndex:section];
return [sectionInfo numberOfObjects];
}
And here my definition of commitEditingStyle, where i remove cell from table and delete data from DB (object type "Transactions" is a subclass of NSManagedObjectContext, that define my model).
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath {
if (editingStyle == UITableViewCellEditingStyleDelete) {
Transactions *trans = (Transactions *)[self.controller objectAtIndexPath:indexPath];
//Delete transaction
[self.context deleteObject:trans];
NSError *error = nil;
[self.context save:&error];
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationTop];
}
}

Answer 1

I find where's the problem.
The delegate is defined in a controller called from a UITabBar. Every time its view appears, a function is called to Fetch data on NSFEtchedResultController(with performFetch) and setup the delegate for the NSFetchedResultControllerDelegate. This way (i don't know exactly why) every time i try to delete or insert cell/section on table, the delegate seems to be duplicated as many time as i opened the controller via UITabBar, thus Delegate function are repeated more than one time creating problem and errors that i described in the question.
To avoid this problem, now i setup Request and Delegate in init function of ViewController and in no other places. This ensure that it set only one reference to delegate and only one Fetch is performed over NSFetchResultController.