Execute code after animation triggered by NSFetchedResultsController has finished - swift

Question

I want to execute a scroll animation after NSFetchedResultsController has finished animating moving a tableview row between sections.
The update of the section happens when I dismiss a view controller. This triggers the animation of the tableview which works fine. after this animation I want the tableview to scroll to the new location. However this does not work the scrolling starts before the animation has finished.
self.dismissViewControllerAnimated(true, completion: {
shoppingItem.category = self.categoryTextField.text // this line triggers the move between sections
dispatch_async(dispatch_get_main_queue(), {
tableView.scrollToRowAtIndexPath(indexPath, atScrollPosition: .Bottom, animated: true)
do {
try self.coreDataStack.context.save()
} catch {
fatalCoreDataError(error)
}
})
})
I realize that the solution lies in managing the threads but I cannot figure out how to set this up correctly.
SOLUTION:
By delaying the scrolling by one second the animation works fine:
var time = dispatch_time(dispatch_time_t(DISPATCH_TIME_NOW), 1 * Int64(NSEC_PER_SEC))
dispatch_after(time, dispatch_get_main_queue(), {
self.indexPathOfChangedItem = self.fetchedResultsController.indexPathForObject(shoppingItem)
self.itemsTableView.scrollToRowAtIndexPath(self.indexPathOfChangedItem, atScrollPosition: .Bottom, animated: true)
})
Note that the definition of the new indexpath, called indexPathOfChangedItem also has to be in the delayed call as this index path is not up to date until the animation triggered by the NSFetchedResultsController is completed.

Answer 1

The FRC isn't doing the animation, it's just observing the change and telling you, your code then tells the table view and it does the animation.
The animation takes no parameters to tell you when it's done or to specify how long it should take :-( raise a radar with Apple.
The simple option is to guess how long the animation runs for and dispatch after a delay to run your scroll after the animation. It's probably trial and error to find the right amount of time to wait, and once found it's unlikely to change / be different for other devices.