title: UIViewController containment crashing
body: <p>I am fiddling with some code to try and get UIViewController containment working (in an iPad app).</p>
  
  <p>The scenario is as follows: I have a view that I'd like to display a second view on top of.  I'd like to have a second (different) UIViewController manage all the interactions with the second view.  The first view will load the second view on the press of a button.  When the button is pressed the following code runs in the first controller:</p>
  
  <pre><code>-(void)displayPropertyView // &lt;-button triggers this
  {
      // Need to instantiate a new view and add it to the main editor view.
      HPSQuestionListController* questionListController = [ [ HPSQuestionListController alloc ] init ];
      [self.view addSubview:questionListController.view];
      [self.view bringSubviewToFront:questionListController.view];
      [self pushViewController:questionListController animated:YES];
  
  }
  -(void)pushViewController:(UIViewController*)controller animated:(BOOL)animated
  {
      [self addChildViewController:controller];
      //[controller didMoveToParentViewController:self];
  
      if (YES)
      {
          [self transitionFromViewController:self 
                            toViewController:controller 
                                    duration:1.0 
                                     options:nil 
                                  animations:^{}
                                  completion:^(BOOL finished){
              [controller didMoveToParentViewController:self];
          }];
      }
  } 
  </code></pre>
  
  <p>The app crashes on the transitionFromViewController line with:</p>
  
  <blockquote>
    <p>Children view controllers  and
     must have a common parent view
    controller when calling -[UIViewController
    transitionFromViewController:toViewController:duration:options:animations:completion:]'</p>
  </blockquote>
  
  <p>Anyone know how to solve this?  My understanding of UIViewController containment is that I can have two controllers managing two views at the same time.  Is this wrong?</p>