title: Animating the presenting view in a UIPresentationController
body: <p>For some context, I recommend reading this:</p>
  
  <p>Very relevant question: <a href="https://stackoverflow.com/questions/24338700/from-view-controller-disappears-using-uiviewcontrollercontexttransitioning">&quot;From View Controller&quot; disappears using UIViewControllerContextTransitioning</a>
  Very relevant answer: <a href="https://stackoverflow.com/a/25901154/751268">https://stackoverflow.com/a/25901154/751268</a></p>
  
  <hr>
  
  <p>I'm trying to implement a custom view controller transition that animates the new view controller to cover half the screen, while simultaneously shrinking the presenting view controller to 90% (centered in the window, underneath the presented view controller).</p>
  
  <p>First, my problem was that <code>viewFromKey:</code> returned <code>nil</code>. To solve that, the answer mentioned:</p>
  
  <blockquote>
    <p>If you want to animate the presenting view controllers's view you should consider using <code>UIModalPresentationFullscreen</code> style or continue using <code>UIModalPresentationCustom</code> and implement your own subclass of <code>UIPresentationController</code> with <code>shouldRemovePresentersView</code> returning YES.</p>
  </blockquote>
  
  <p>I did that, and <code>viewFromKey:</code> doesn't return <code>nil</code> anymore, but now the presenting view controller disappears completely (which makes sense considering I explicitly say it should by implementing <code>shouldRemovePresentersView</code>).</p>
  
  <p>I add the presenting view controller's view to the container view, but it still gets removed. Is there anything else I should be doing to get this working?</p>
  
  <p>Here's some relevant code:</p>
  
  <pre><code>UIView *fromView = [transitionContext viewForKey:UITransitionContextFromViewKey
  UIView *toView = [transitionContext viewForKey:UITransitionContextToViewKey];
  
  BOOL show = self.isPresentation;
  UIView *menuView = show ? toView : fromView;
  UIView *backView = show ? fromView : toView;
  
  UIView *containerView = [transitionContext containerView];
  
  [containerView addSubview:backView];
  [containerView addSubview:dimmedView];
  [containerView addSubview:menuView];
  
  // Adjust transforms, alpha and perform animations
  </code></pre>
  
  <p>I thought that by returning <code>YES</code> from <code>shouldRemovePresentersView</code> and manually adding it to the <code>containerView</code>, that should fix the issue, but <code>backView</code> gets removed anyway...</p>