UITableView row delete crashes app - ios

Question

I have a Core Data based table view that has a simple delete method. It is straightforward code that can be found in countless tutorials, however, it crashes the app with the following message:
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 (2) 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).'
The delete method is as follows:
- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath
{
if (editingStyle == UITableViewCellEditingStyleDelete) {
// get garden to delete, delete it through Core Data
Garden *gardenToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSLog(#"Garden name: %#", gardenToDelete.gardenName);
[self.managedObjectContext deleteObject:gardenToDelete];
[self.managedObjectContext save:nil];
[self.tableView beginUpdates];
[self.tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationRight];
[self.tableView endUpdates];
}
}
I have spent hours rearranging the code, removing the beginUpdate and endUpdate calls, checking other solutions. Help is greatly appreciated.

Answer 1

You just need to delete the object from your NSFetchedResultsController, the fetched results controller will then update the table view assuming you've implemented the delegate methods as described in the docs. You shouldn't touch the table view rows, the NSFetchedResultsControllerDelegate does all of that.
-(void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath{
if (editingStyle == UITableViewCellEditingStyleDelete) {
// deleting cell from fetched results contoller
Garden *gardenToDelete = [self.fetchedResultsController objectAtIndexPath:indexPath];
NSLog(#"Garden name: %#", gardenToDelete.gardenName);
[self.managedObjectContext deleteObject:gardenToDelete];
[self.managedObjectContext save:nil];
}
}

Answer 2

Do you implement - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section with a return value with NSFetchedResultsController? After you do save, self.fetchedResultsController will refresh, but make sure all of the dataSource of tableView return value is depended on self.fetchedResultsController.

Answer 3

Do you implement these methods:
- (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;
// my comment: mapIndexPathFromFetchResultsController function, I just use to get indexPath. You can remove it
indexPath = [self mapIndexPathFromFetchResultsController:indexPath];
newIndexPath = [self mapIndexPathFromFetchResultsController:newIndexPath];
switch(type) {
case NSFetchedResultsChangeInsert:
{
[tableView insertRowsAtIndexPaths:#[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
}
case NSFetchedResultsChangeDelete:
{
[tableView deleteRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationFade];
break;
}
case NSFetchedResultsChangeUpdate:
{
UITableViewCell *cell;
cell = [tableView cellForRowAtIndexPath:indexPath];
if (cell != nil)
{
// my comment: just use the same with cellForRowAtIndexPath
// - (void)syncViewConfigureCell:(UITableViewCell *)cell {
// cell.textLabel.text = #""; etc. }
[self syncViewConfigureCell:cell];
}
break;
}
case NSFetchedResultsChangeMove:
{
[tableView deleteRowsAtIndexPaths:#[indexPath] withRowAnimation:UITableViewRowAnimationFade];
[tableView insertRowsAtIndexPaths:#[newIndexPath] 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 {
// The fetch controller has sent all current change notifications, so tell the table view to process all updates.
[self.tableView endUpdates];
}