How to check an UIImageView is out of the visible area of the UIScrollView?

Question

In the UIScrollView, it holds numerous UIImageView objects.

How to check an UIImageView is out of the visible area of the UIScrollView ?

Can an UIImageView observe itself for moving away from the visible area ?

Thanks.

Answer 1

CGRect visibleRect;
visibleRect.origin = scrollView.contentOffset;
visibleRect.size = scrollView.bounds.size;

BOOL imageViewIsVisible = CGRectIntersectsRect(visibleRect, imageView.frame);

You can observe it in UIScrollViewDelegate's scrollViewDidScroll: method