Getting the visible rect of an UIScrollView's content

Question

How can I go about finding out the rect (CGRect) of the content of a displayed view that is actually visible on screen.

myScrollView.bounds

Answer 1

Swift 4.0:

My answer adapts Trenskow's answer to Swift 4.0:

let visible = scrollView.convert(scrollView.bounds, to: subView)

where scrollView is the view of the scroll, and subView is the view inside scrollView which is zoomable and contains all the contents inside the scroll.

Answer 2

Answering my own question, mostly thanks to Jim Dovey's answer, which didn't quite do the trick, but gave me the base for my answer:

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

float theScale = 1.0 / scale;
visibleRect.origin.x *= theScale;
visibleRect.origin.y *= theScale;
visibleRect.size.width *= theScale;
visibleRect.size.height *= theScale;

The main difference is that the size of the visibleRect ought to be scrollView.bounds.size, rather than scrollView.contentSize which is the size of the content view. Also simplified the math a bit, and didn't quite see the use for the isless() which would break the code whenever it's greater.

Answer 3

a little more general solution would be:

 [scrollView convertRect:scrollView.bounds
                             toView:[scrollView.delegate viewForZoomingInScrollView:scrollView]];

Answer 4

Shorter version:

CGRect visibleRect = CGRectApplyAffineTransform(scrollView.bounds, CGAffineTransformMakeScale(1.0 / scrollView.zoomScale, 1.0 / scrollView.zoomScale));

I'm not sure if this is defined behavior, but almost all UIView subclasses have the origin of their bounds set to (0,0). UIScrollViews, however, have the origin set to contentOffset.

Answer 5

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

Answer 6

I don't think that a UIScrollView gives you that rectangle directly, but I think you have all the necessary items to calculate it.

A combination of the bounds, the contentOffset and the zoomScale should be all you need to create the rectangle you are looking for.