title: Custom QLPreviewController or UIDocumentInteractionController that can intercept touch events
body: <p>Ok, so what I am trying to do is create a Document Viewer that is similar this picture:
  <img src="https://i.stack.imgur.com/0hwMH.png" alt="enter image description here"></p>
  
  <p>Basically what should happen is, when the screen is tapped anywhere, the top and bottom bar will appear.  Tap again and they disappear. </p>
  
  <p>I have subclassed <code>QLPreviewController</code> and have managed to leverage the (top) navigation bar that already comes with <code>QLPreviewController</code>.  This works fine.  Now I need to get the bottom bar to display whenever the top bar is displayed.  I can add a <code>UIToolbar</code> to the bottom of the page, but I need to intercept the touch events so I can hide/unhide the bottom bar.  I cannot seem to figure out how to get it to work.  I tried adding a <code>UITapGestureRecognizer</code> to the view of the <code>QLPreviewController</code> subclass itself to no luck.  I also tried creating an overlay <code>UIView</code> that has a <code>UITapGestureRecognizer</code> but that prevented the user form interacting with the document underneath.</p>
  
  <p>Anyone have any ideas at all on how to do this? Thanks in advance!</p>