How to get notified when scrollToRowAtIndexPath finishes animating
You can use the table view delegate's scrollViewDidEndScrollingAnimation:
method. This is because a UITableView
is a subclass of UIScrollView
and UITableViewDelegate
conforms to UIScrollViewDelegate
. In other words, a table view is a scroll view, and a table view delegate is also a scroll view delegate.
So, create a scrollViewDidEndScrollingAnimation:
method in your table view delegate and deselect the cell in that method. See the reference documentation for UIScrollViewDelegate
for information on the scrollViewDidEndScrollingAnimation:
method.
try this
[UIView animateWithDuration:0.3 animations:^{
[yourTableView scrollToRowAtIndexPath:indexPath
atScrollPosition:UITableViewScrollPositionTop
animated:NO];
} completion:^(BOOL finished){
//do something
}];
Don't forget to set animated to NO, the animation of scrollToRow will be overridden by UIView animateWithDuration.
Hope this help !
To address Ben Packard's comment on the accepted answer, you can do this. Test if the tableView can scroll to the new position. If not, execute your method immediately. If it can scroll, wait until the scrolling is finished to execute your method.
- (void)someMethod
{
CGFloat originalOffset = self.tableView.contentOffset.y;
[self.tableView scrollToRowAtIndexPath:path atScrollPosition:UITableViewScrollPositionMiddle animated:NO];
CGFloat offset = self.tableView.contentOffset.y;
if (originalOffset == offset)
{
// scroll animation not required because it's already scrolled exactly there
[self doThingAfterAnimation];
}
else
{
// We know it will scroll to a new position
// Return to originalOffset. animated:NO is important
[self.tableView setContentOffset:CGPointMake(0, originalOffset) animated:NO];
// Do the scroll with animation so `scrollViewDidEndScrollingAnimation:` will execute
[self.tableView scrollToRowAtIndexPath:path atScrollPosition:UITableViewScrollPositionMiddle animated:YES];
}
}
- (void)scrollViewDidEndScrollingAnimation:(UIScrollView *)scrollView
{
[self doThingAfterAnimation];
}
You can include the scrollToRowAtIndexPath:
inside a [UIView animateWithDuration:...]
block which will trigger the completion block after all included animations conclude. So, something like this:
[UIView
animateWithDuration:0.3f
delay:0.0f
options:UIViewAnimationOptionAllowUserInteraction
animations:^
{
// Scroll to row with animation
[self.tableView scrollToRowAtIndexPath:indexPath
atScrollPosition:UITableViewScrollPositionTop
animated:YES];
}
completion:^(BOOL finished)
{
// Deselect row
[self.tableView deselectRowAtIndexPath:indexPath animated:YES];
}];
Swift 5
The scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView)
delegate method is indeed the best way to execute a completion on a scroll-to-row animation but there are two things worth noting:
First, the documentation incorrectly says that this method is only called in response to setContentOffset
and scrollRectToVisible
; it's also called in response to scrollToRow
(https://developer.apple.com/documentation/uikit/uiscrollviewdelegate/1619379-scrollviewdidendscrollinganimati).
Second, despite the fact that the method is called on the main thread, if you're running a subsequent animation here (one after the scroll has finished), it will still hitch (this may or may not be a bug in UIKit). Therefore, simply dispatch any follow-up animations back onto the main queue which just ensures that the animations will begin after the end of the current main task (which appears to include the scroll-to-row animation). Doing this will give you the appearance of a true completion.
func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
DispatchQueue.main.async {
// execute subsequent animation here
}
}