UIScrollView scrollRectToVisible:animated: is there a way that a method can be called when animation ends

Question

Is there a way to know when the animation has end and uiscrollview has come to rest.

Profundity

Regarding this very old question, nowadays there are THREE situations which must be covered. It's one of the strangest and most difficult issues in iOS. :/ – Languorous

Answer 1

Yup use scrollViewDidEndScrollingAnimation

Korella

It doesn't get called everytime ex. when scrollRectToVisible() is called inside traitCollationDidChange – Patently

This is wrong, there are three separate cases to cover. – Languorous

I agree with @Fattie's comment because there are multiple scenarios which scrolling can end. This answer is not as good as Fattie's answer below. – Boat

@Languorous Yes, and for some reason SO bot decides to remove 1 reputation from me. Anyway, just wanted to thank you for your answer. – Boat

Answer 2

I do it like this because sometimes using the delegate isn't practical for me, like if i'm doing it in UIViewController transition:

[UIView animateWithDuration:0.3 animations:^{
    [scrollView setContentOffset:CGPointMake(0, -scrollView.contentInset.top) animated:NO];
} completion:^(BOOL finished) {
    // This is called when it's complete
}];

Deluxe

Exactly! I also used the same code only then it worked as per expectation. – Sate

I put my cell modification code into the completion but my animation and completion are executing line by line. not working as expected :( – Ogg

unfortunately, this will literally crash in many circumstances. – Languorous

Answer 3

Implement UIScrollViewDelegate delegate methods for your UIScrollView the following way:

Use scrollViewDidEndScrollingAnimation: to detect when the scrolling animation concludes when you've initiated the scrolling by calling setContentOffset:animated: or scrollRectToVisible:animated: methods (with animated:YES).

If you want to monitor scroll view motion that's been initiated by touch gestures, use scrollViewDidEndDecelerating: method, which is called when the scrolling movement comes to a halt.

Cloninger

for anyone googling here, this very old answer is now incorrect - thanks, Apple! :/ – Languorous

Answer 4

You need to cover THREE (!) cases. Thanks, Apple.

// do note that you need all three of the following

public func scrollViewDidEndScrollingAnimation(_ s: UIScrollView) {
    // covers case setContentOffset/scrollRectToVisible
    fingerOrProgrammaticMoveDone()
}

public func scrollViewDidEndDragging(_ s: UIScrollView, willDecelerate d: Bool) {
    if decelerate == false {
        // covers certain cases of user finger
        fingerOrProgrammaticMoveDone()
    }
}

public func scrollViewDidEndDecelerating(_ s: UIScrollView) {
    // covers certain cases of user finger
    fingerOrProgrammaticMoveDone()
}

(Be careful to not forget the extra "if" clause in the middle one.)

Then in fingerOrProgrammaticMoveDone() , do what you need.

A good example of this is the nightmare of handling paged scrolling. It is very, very hared to know what page you are on.

Languorous

Answer 5

scrollViewDidEndDecelerating: UIScrollView delegate method is called when scrollView stops completely.

Stylist