Question

I have a Core Data app with a tab-bar controller that displays 2 view controllers. If I add something in the first tab’s view controller, it should display in the 2nd tab’s VC. Both VCs are based off a NSFetchedResultsController which is based off the same entity; the only difference is that one has a predicate and the 2nd VC doesn’t.

This works fine for the normal template, and when data is added from the 1st VC, it gets updated instantly in the 2nd tab using controllerWillChangeContent and controllerDidChangeContent. The problem is that if the user adds or deletes any rows in the 1st VC, when the user comes to the 2nd tab they don’t see the rows animatedly inserted or deleted… everything’s already there.

What I would like to do, in the 2nd tab’s VC, is delay calling the [self.tableView endUpdates] (which causes the animated inserting/deleting of rows in the table) till the user actually goes to that tab, in that VC’s viewWillAppear. I’ve tried this, but doesn’t seem to work:

- (void)controllerDidChangeContent:(NSFetchedResultsController *)controller
{
        tableviewUpdates = TRUE;
}

- (void)viewWillAppear:(BOOL)animated
{
    [super viewWillAppear:animated];
    if (tableviewUpdates) {
        tableviewUpdates = FALSE;
        [self.tableView endUpdates];
    }
}

This works if adding one row at a time and then switching to the 2nd tab, but not if I add multiple rows in the 1st tab and then switch.
Any help would be appreciated.

Answer 1

You’re working against the purpose of the NSFetchedResultsController which is to make updating the tableview automatic and effortless.

I’m pretty sure, however, that if you override all the FRC delegate methods you can block all the automatic updates.

You might want to rethink this design. Are users really going to expect to see changes in one view reenacted in a second? Will they understand they are watching a rewind of the previous changes or will they intuitively think that the app is doing something to their data on its own?

The standard UI grammar teaches users to expect that one change animates once and then subsequently just shows up in a standard display. I would suggest you test this design with naive users carefully before deploying such a non-standard interface.