当使用2个相同的NSIndexPath调用NSFetchedResultsChangeMove时，如何保持单元格处于选中状态？

Question

If I click on a cell and a background Core Data refresh happens, my cell gets deselected.

After investigation, my NSFetchedResultsControllerDelegate 's implementation of controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: gets called with a type of NSFetchedResultsChangeMove but indexPath and newIndexPath are identical (ie same row/section values).

The NSFetchedResultsChangeUpdate type doesn't get called.

My implementation of controller:didChangeObject:atIndexPath:forChangeType:newIndexPath: is the typical one provided in Apple's documentation. I believe that switching from:

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath {

    ...

    switch(type) {

        ...

        case NSFetchedResultsChangeMove:
            [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
            [tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            break;
    }
}

to:

- (void)controller:(NSFetchedResultsController *)controller didChangeObject:(id)anObject
       atIndexPath:(NSIndexPath *)indexPath forChangeType:(NSFetchedResultsChangeType)type
      newIndexPath:(NSIndexPath *)newIndexPath {

    ...

    switch(type) {

        ...

        case NSFetchedResultsChangeMove:
            if (indexPath.section != newIndexPath.section || indexPath.row != newIndexPath.row) {
                [tableView deleteRowsAtIndexPaths:@[indexPath] withRowAnimation:UITableViewRowAnimationFade];
                [tableView insertRowsAtIndexPaths:@[newIndexPath] withRowAnimation:UITableViewRowAnimationFade];
            }
            break;
    }
}

would solve my problem.

My question is: is this fix correct or do I miss something that could explain why my update is of the NSFetchedResultsChangeMove type?

Answer 1

My problem was that I was that I was assigning values to NSManagedObject instances that were the same as before. ie, if foo.bar was 2, I would call the API and call a new foo.bar = 2 assignment on my object. Even though, values were identical, Core Data was still considering the value had changed.

It is still weird that I got a NSFetchedResultsChangeMove type instead of a NSFetchedResultsChangeUpdate type but heh.

What I did to resolve this is:

if ([object.changedValues count] == 0) {
    // Reverting changed on object
    [context refreshObject:object mergeChanges:NO]
}

At the end of each update, rather than comparing attributes one by one.