check if UIView is in UIScrollView visible state

Question

What is the easiest and most elegant way to check if a UIView is visible on the current UIScrollView's contentView? There are two ways to do this, one is involving the contentOffset.y position of the UIScrollView and the other way is to convert the rect area?

Answer 1

If you're trying to work out if a view has been scrolled on screen, try this:

    CGRect thePosition =  myView.frame;
    CGRect container = CGRectMake(scrollView.contentOffset.x, scrollView.contentOffset.y, scrollView.frame.size.width, scrollView.frame.size.height);
    if(CGRectIntersectsRect(thePosition, container))
    {
        // This view has been scrolled on screen
    }

Answer 2

Swift 5: in case that you want to trigger an event that checks that the entire UIView is visible in the scroll view:

extension ViewController: UIScrollViewDelegate {

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if scrollView.bounds.contains(targetView.frame) {
            // entire UIView is visible in scroll view
        }
    }

}

Answer 3

Implement scrollViewDidScroll: in your scroll view delegate and calculate manually which views are visible (e.g. by checking if CGRectIntersectsRect(scrollView.bounds, subview.frame) returns true.