How to implement NSFetchedResultsController delegate when multiple row is on deletion? - ios

Question

Two items is deleted.
func controller(controller: NSFetchedResultsController!, didChangeObject anObject: AnyObject!, atIndexPath indexPath: NSIndexPath!, forChangeType type: NSFetchedResultsChangeType, newIndexPath: NSIndexPath!) {
switch(type) {
case .Delete:
tableView.deleteRowsAtIndexPaths([indexPath], withRowAnimation: .Fade)
default:
break
}
}
At deletion line I get this error:
CoreData: error: Serious application error. Exception was caught
during Core Data change processing. This is usually a bug within an
observer of NSManagedObjectContextObjectsDidChangeNotification.
Invalid update: invalid number of rows in section 0. The number of
rows contained in an existing section after the update (0) must be
equal to the number of rows contained in that section before the
update (2), plus or minus the number of rows inserted or deleted from
that section (0 inserted, 1 deleted) and plus or minus the number of
rows moved into or out of that section (0 moved in, 0 moved out). with
userInfo (null)
*** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Invalid update: invalid
number of rows in section 0. The number of rows contained in an
existing section after the update (0) must be equal to the number of
rows contained in that section before the update (2), plus or minus
the number of rows inserted or deleted from that section (0 inserted,
1 deleted) and plus or minus the number of rows moved into or out of
that section (0 moved in, 0 moved out).'

Answer 1

You need to 'batch' the updates by also implementing the controllerWillChangeContent and controllerDidChangeContent delegate methods as follows (although sorry these are Obj-c):
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
[self.tableView beginUpdates];
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}