Question

I want to fade-out a view as it is scrolling inside a parent UIScrollview. When the fade-out animation begins, the scroll view stops scrolling. It jumps to the correct position when the fade is complete.

My fade-out is achieved with animateWithDuration and block objects, triggered upon a page-change I detect in scrollViewWillBeginDragging.

Does anyone know how to make them both happen simultaneously? Just to be clear, I am not ‘animating’ the UIScrollView scrolling – rather it is happening via user interaction of swiping.

EDIT:

Here is the code I’m using to fade the UIView. This code is in a UIViewController derived class, which is the delegate for a UIScrollView. When the user starts dragging his finger, I want to fade out the subView. But when the user starts draggin a finger, the subview fades and the scrolling stops. After the subView has completely faded out, the the scroll view will then snap to the location where the user’s finger is.

-(void)scrollViewWillBeginDragging:(UIScrollView*)scrollView
{
    [UIView animateWithDuration:0.5
        animations:^
        {
            self.subView.alpha = 0.0f;
        }
        completion:^(BOOL finished) { }];
}

Answer 1

very interesting … I’ve checked this out, and yes, i have the same effect … Well, it seems that the animateWithDuration somehow blocks the main thread … which is not logical, and the documentation doesn’t say anything about it either ..
However there is an easy workaround, something similar to this: (i’ve set the animation duration to 3 so i can see that it’s working while i’m moving my scroll view 🙂 …)

[UIView beginAnimations:@"FadeAnimations" context:nil];
[UIView setAnimationDuration:3]; 

self.subview.alpha = 0.0f;

[UIView commitAnimations];