title: Nesting UIPageViewController in a UINavigationController shows only one page
body: <p>I've spend hours on this and can't get it to work. Hope that someone can help me. </p>
  
  <p>I have a UIPageViewController which works perfectly when I add it to my default view when the application starts. This is what I do:</p>
  
  <pre><code>//Step 1
  //Instantiate the UIPageViewController.
  self.pageViewController = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStylePageCurl
                                                            navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];
  
  //Step 2:
  //Assign the delegate and datasource as self.
  self.pageViewController.delegate = self;
  self.pageViewController.dataSource = self;
  
  //Step 3:
  //Set the initial view controllers.
  ContentViewController *contentViewController = [[ContentViewController alloc] initWithNibName:@"ContentViewController" bundle:nil];
  contentViewController.labelContents = [self.modelArray objectAtIndex:0];
  NSArray *viewControllers = [NSArray arrayWithObject:contentViewController];
  [self.pageViewController setViewControllers:viewControllers
                                    direction:UIPageViewControllerNavigationDirectionForward
                                     animated:NO
                                   completion:nil];
  
  
  [self addChildViewController:self.pageViewController];
  [self.view addSubview: self.pageViewController.view];
  </code></pre>
  
  <p>Now I want to use a navigation controller in my initial view which then pushes the UIPageViewController on the stack, when the user clicks on a button. This works too, but when I'm in landscape mode the UIPageViewController shows only one page (which is horizontally streched) and not two, as it should be. I need to rotate the device to portrait and then back to landscape mode to force the UIPageViewController to show both pages. 
  I'm adding the UIPageViewController to the navigation controller with:</p>
  
  <pre><code>[self.navController pushViewController:self.pageViewController animated:NO];
  </code></pre>
  
  <p>When i debug my code I see that without the navigation controller the delegate methods of the UIPageViewController are called on startup. When I push the UIPageViewController on the navigation controller they're not called until I rotate the device.</p>
  
  <p>Does anyone know how to solve this? Thanks in advance for any help/tips on this.</p>