title: UIView in UIScrollview. frame.origin not changing on scrolling, can't detect collision
body: <p>I have a screen containing:</p>
  
  <ul>
  <li>UIView A</li>
  <li>UIScrollView, which contains UIView B</li>
  </ul>
  
  <p>The UIScrollView overlaps with UIView A (up until about halfway through it), allowing me to "drag" UIView B and make it overlap it with UIView A. This is so that when I let go of it, UIView B bounces nicely back into its original position (I don't want to be able to drag it all around the screen, just from its starting point onto UIView A)</p>
  
  <p>Now, I'm trying to detect a collision when the UIViews overlap. However, none is ever detected. I am using convertRect:toView: to get coordinates on the same system, but from tracing UIView B's coordinates in its touchesMoved I see that "dragging" (scrolling the UIScrollView, really) doesn't affect its frame's origin coordinates. They are the same in touchedBegan as they are every time touchedMoved fires.</p>
  
  <p>I'm assuming this is because UIView B isn't really moving anywhere, UIScrollView is, meaning that the UIView's origin point is always the same, even if its absolute coordinates aren't. Any suggestion on how to handle this?</p>
  
  <p><img src="https://i.stack.imgur.com/BcIud.jpg" alt=""></p>