NSFetchedResultsController: using of NSManagedObjectContext during update brings to crash
- by Kentzo
Here is the interface of my controller class:
@interface ProjectListViewController : UITableViewController <NSFetchedResultsControllerDelegate> {
NSFetchedResultsController *fetchedResultsController;
NSManagedObjectContext *managedObjectContext;
}
@end
I use following code to init fetchedResultsController:
if (fetchedResultsController != nil) {
return fetchedResultsController;
}
// Create and configure a fetch request with the Project entity.
NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription entityForName:@"Project" inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];
// Create the sort descriptors array.
NSSortDescriptor *projectIdDescriptor = [[NSSortDescriptor alloc] initWithKey:@"projectId" ascending:YES];
NSArray *sortDescriptors = [[NSArray alloc] initWithObjects:projectIdDescriptor, nil];
[fetchRequest setSortDescriptors:sortDescriptors];
// Create and initialize the fetch results controller.
NSFetchedResultsController *aFetchedResultsController = [[NSFetchedResultsController alloc] initWithFetchRequest:fetchRequest
managedObjectContext:managedObjectContext
sectionNameKeyPath:nil
cacheName:nil];
self.fetchedResultsController = aFetchedResultsController;
fetchedResultsController.delegate = self;
As you can see, I am using the same managedObjectContext as defined in my controller class
Here is an adoption of the NSFetchedResultsControllerDelegate protocol:
- (void)controllerWillChangeContent:(NSFetchedResultsController *)controller {
// The fetch controller is about to start sending change notifications, so prepare the table view for updates.
[self.tableView beginUpdates];
}
- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type newIndexPath:(NSIndexPath *)newIndexPath {
UITableView *tableView = self.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:
[self _configureCell:(TDBadgedCell *)[tableView cellForRowAtIndexPath:indexPath] atIndexPath:indexPath];
break;
case NSFetchedResultsChangeMove:
if (newIndexPath != nil) {
[tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:[NSArray arrayWithObject:newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
}
else {
[tableView reloadSections:[NSIndexSet indexSetWithIndex:indexPath.section] withRowAnimation:UITableViewRowAnimationFade];
}
break;
}
}
- (void)controller:(NSFetchedResultsController *)controller didChangeSection:(id <NSFetchedResultsSectionInfo>)sectionInfo atIndex:(NSUInteger)sectionIndex forChangeType:(NSFetchedResultsChangeType)type {
switch(type) {
case NSFetchedResultsChangeInsert:
[self.tableView insertSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
case NSFetchedResultsChangeDelete:
[self.tableView deleteSections:[NSIndexSet indexSetWithIndex:sectionIndex] withRowAnimation:UITableViewRowAnimationFade];
break;
}
}
- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller {
[self.tableView endUpdates];
}
Inside of the _configureCell:atIndexPath: method I have following code:
NSFetchRequest *issuesNumberRequest = [NSFetchRequest new];
NSEntityDescription *issueEntity = [NSEntityDescription entityForName:@"Issue" inManagedObjectContext:managedObjectContext];
[issuesNumberRequest setEntity:issueEntity];
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"projectId == %@", project.projectId];
[issuesNumberRequest setPredicate:predicate];
NSUInteger issuesNumber = [managedObjectContext countForFetchRequest:issuesNumberRequest error:nil];
[issuesNumberRequest release];
I am using the managedObjectContext again.
But when I am trying to insert new Project, app crashes with following exception:
Assertion failure in -[UITableView
_endCellAnimationsWithContext:], /SourceCache/UIKit_Sim/UIKit-984.38/UITableView.m:774
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 (4)
must be equal to the number of rows
contained in that section before the
update (4), plus or minus the number
of rows inserted or deleted from that
section (1 inserted, 0 deleted).'
Fortunately, I've found a workaround: if I create and use separate NSManagedObjectContext inside of the _configureCell:atIndexPath: method app won't crash!
I only want to know, is this behavior correct or not?
