How can I make deleteRowsAtIndexPaths: work with GenericTableViewController?

Question

I'm using Matt Gallagher's GenericTableViewController idea for controlling my UITableViews. My datasource is a NSFetchedResultsController.

http://cocoawithlove.com/2008/12/heterogeneous-cells-in.html

Everything is working fine, until I try to delete a cell.

I have the following code in my View Controller:

- (void)tableView:(UITableView *)tableView commitEditingStyle:(UITableViewCellEditingStyle)editingStyle forRowAtIndexPath:(NSIndexPath *)indexPath { if (editingStyle == UITableViewCellEditingStyleDelete) { // Delete the managed object. NSManagedObjectContext *context = [wineryController managedObjectContext]; [context deleteObject:[wineryController objectAtIndexPath:indexPath]]; NSError *error; if (![context save:&error]) { // Handle the error. } [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; } }

The final line crashes with the rather verbose explanation in the console:

*** 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 (5) must be equal to the number of rows contained in that section before the update (5), plus or minus the number of rows inserted or deleted from that section (0 inserted, 1 deleted).'

OK, I understand what it is saying... a row is not getting deleted (I would assume) because I'm not forwarding some message to the right place (since I have moved some code from its 'normal' location)... anyone have any idea which one? I am totally stumped on this one.

Community · Accepted Answer · 2017-05-23 12:34:00Z

Well, bah. I just found this answer, which is not the same, but got me headed in the right direction. I'll leave this here for anyone in the future having similar troubles.

The key is to wrap the deleteRowsAtIndexPaths with begin and end tags, and force the model to update within the same block, resulting in:

[tableView beginUpdates]; [self constructTableGroups]; [tableView deleteRowsAtIndexPaths:[NSArray arrayWithObject:indexPath] withRowAnimation:UITableViewRowAnimationFade]; [tableView endUpdates];

This caused the issue to go away, and the animations to work just perfectly.

You're allowed to modify the data source before the animation block. The error that you saw is indicating that you haven't changed the data source before animating the delete. Make sure that the data source is in the final state (after the deletions) before you animate the removal of those rows.
I always forget about this... why doesn't the XCode template code include these lines?

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