title: Allow only one UIView to be touched
body: <p>I have three <code>UIViews</code>:</p>
  
  <p><img src="https://i.stack.imgur.com/rXUjb.png" alt="views"></p>
  
  <p><code>B1</code> and <code>B2</code> are subviews of <code>A</code>.</p>
  
  <p><code>B1</code> and <code>B2</code> may have one or more subviews.</p>
  
  <p>I want that only one <strong>view can be touched at the same time.</strong></p>
  
  <p>For example:</p>
  
  <p>The user touches <code>B1</code> (or one of its subviews) with the first finger, and then, without releasing it, touches <code>B2</code> (or one of its subviews) with the second finger. Now, <code>B1</code> should receive all events in its bounds, but not <code>B2</code>. Same thing the other way around.</p>
  
  <p>Is this possible to accomplish <strong>without subclassing any of these views</strong>?</p>
  
  <p>If not, what's the easiest/cleanest way to do it?</p>
  
  <p><strong>Edit:</strong></p>
  
  <p>About <code>exclusiveTouch</code> and <code>multipleTouchEnabled</code>:</p>
  
  <p>These properties are not valid for my problem.</p>
  
  <p><code>multipleTouchEnabled</code>: Only determines whether or not multi-touch-events are delivered <strong>in the same view</strong>. So disabling multi-touch on view A (which is the default anyways) will not block view B1 and B2 from receiving touch events at the same time.</p>
  
  <p><code>exclusiveTouch</code>: Doesn't work either. As far as I have understood, <code>exclusiveTouch</code> only works <strong>inside the frame of the view</strong>. So setting <code>exclusiveTouch</code> on view B1 and B2 has no effect.
  See these two stackoverflows for reference:</p>
  
  <p><a href="https://stackoverflow.com/questions/3946147/why-is-uiview-exclusivetouch-property-not-blocking">Why is UIView exclusiveTouch property not blocking?</a></p>
  
  <p><a href="https://stackoverflow.com/questions/843338/why-doesnt-uiview-exclusivetouch-work">Why doesn&#39;t UIView.exclusiveTouch work?</a></p>