Cancel UIScrollView bounce after dragging

Question

I have a horizontal UIScrollView. I want to do a variation of the "pull-to-reset" animation, where I pull all the way past the right edge of the scroll view's content size, release my finger, and have the scroll view fly back to (0, 0) content offset.

My delegate method looks like this:

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
    //check if it exceeds a certain critical value
    if (scrollView.contentOffset.x - (scrollView.contentSize.width - IMAGE_WIDTH) > 80) {
        [self doAnimatedScrollTo:CGPointMake(0, 0)];
    }
}

where doAnimatedScrollTo: is a custom animation method necessary because I want to control the duration of the animation.

While this works, it seems that the animation is queued up. The UIScrollView "bounce" animation happens first, then my animation occurs.

Is there a way to cancel the bounce animation, keep the content offset from "snapping" back, and then perform my animation?

did you try unchecking the bounce property on the attribute inspector? — jcesarmobile, Feb 15 '13 at 11:10
@jcesar nope, because I want the bounce property explicitly. I just don't want the 2nd half of the animation from executing - ie. the "bounce back". — 1actobacillus, Feb 15 '13 at 11:14
Then I don't think it's possible. If you use the bounce you have to use the full bounce. Maybe if you create a subclass you can change the full animation — jcesarmobile, Feb 15 '13 at 11:22

score 3 · Accepted Answer · answered Sep 05 '13 at 10:13

try this

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate {
  //check if it exceeds a certain critical value
  if (scrollView.contentOffset.x - (scrollView.contentSize.width - IMAGE_WIDTH) > 80) {
    [scrollView setContentOffset:CGPointMake(0, 0) animated:YES];
  }
}

Kamil.S · Answer 2 · 2013-10-16T16:13:55.107

I accomplished cancelling the bounce back animation of a UIScrollView.

I wanted to leave the default behaviour during a rapid scroll to the top when it bounces. However if scrollview is already at the top and then the user pulls it down and releases (analogous to pull to refresh) I wanted to take the control over the bounce back and do something custom.

In scrollview delegate I track the initial position:

- (void)scrollViewWillBeginDragging:(UIScrollView *)scrollView
{
    if (scrollView.contentOffset.y < 0.1)
    {
        isPullingTop = YES;
    }
}

In scrollview delegate detect if the flag is set and scrollview is dragged enough

- (void)scrollViewDidEndDragging:(UIScrollView *)scrollView willDecelerate:(BOOL)decelerate
{
    if (isPullingTop && scrollView.contentOffset.y < -30) {

        overrideBounce = YES;
    }
    isPullingTop = NO;
}

I subclass scrollview and override the setContentOffset:

-(void)setContentOffset:(CGPoint)contentOffset
{
    if (!overrideBounce)
    {
        [super setContentOffset:contentOffset];
    }
    else
    {
        //customs stuff goes here , for example an animation
        overrideBounce = NO;
    }
}

Cancel UIScrollView bounce after dragging

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