How to execute code after an animation without using the completion block? - ios

Question

I would like to execute some code after a built-in animation is completed.
I have a UITableView with a lot of cells/rows. Sometimes, when I do some operations and then I need to scroll to the top of my tableView. For that I use :
tableView.scrollToRowAtIndexPath(NSIndexPath(forRow: 0, inSection: 0), atScrollPosition: UITableViewScrollPosition.Top, animated: true)
But I need to perform some code once the top is reached, such a simple select and deselect of the 1rst row.
I implemented func scrollViewDidEndScrollingAnimation(scrollView: UIScrollView) from the UIScrollViewDelegate. It works fine (more or less, sometimes the animation isn't really smooth and we don't see the select/deselect "animation") except when I am already at the top of the tableView, then scrollViewDidEndScrollingAnimation isn't called.
So is there a way to execute some code once scrollToRowAtIndexPath:atScrollPosition:animated has been called?
EDIT:
When I'm talking about doing some operations, I'm talking about moving a row using moveRowAtIndexPath:toIndexPath from UITableView.
So when scrolling is needed it's fine, both animations take about the same amount of time. But when no scroll is needed, then the execution of the code I want to do after the animation, starts at the same time than the animation

Answer 1

You can use this Swift code which I adapted from an old Objective-C answer to scroll the view.
// First, test whether the tableView needs to scroll to the new position
var originalOffset = tableView.contentOffset.y;
tableView.scrollToRowAtIndexPath(NSIndexPath(forRow: 0, inSection: 0), atScrollPosition: UITableViewScrollPosition.Top, animated: false)
var offset = tableView.contentOffset.y;
if (originalOffset == offset) {
// No animation is needed since its already there
doThingAfterAnimation();
} else {
// We know it will scroll to a new position
// Return to originalOffset. animated:NO is important
tableView.setContentOffset(CGPointMake(0, originalOffset), animated: false);
// Do the scroll with animation so `scrollViewDidEndScrollingAnimation:` will execute
tableView.scrollToRowAtIndexPath(NSIndexPath(forRow: 0, inSection: 0), atScrollPosition: UITableViewScrollPosition.Top, animated: true)
}
And then of course:
func scrollViewDidEndScrollingAnimation(scrollView: UIScrollView) {
doThingAfterAnimation();
}