title: viewControllerBeforeViewController is not called every time in UIPageViewController
body: <p>I have implemented <code>UIPageViewController</code> in my application.</p>
  
  <p>I have implemented two <code>delegate</code> methods which returns view for particular Index.</p>
  
  <p>And Also i am detecting forward and backward direction from these methods.</p>
  
  <pre><code>  - (UIViewController *)pageViewController:(UIPageViewController *)pageViewController  viewControllerBeforeViewController:(UIViewController *)viewController
  
    - (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController
  </code></pre>
  
  <p>Now the problem is that sometimes <code>viewControllerBeforeViewController</code> and <code>viewControllerAfterViewController</code> are not called but Pagination works fine. Due to this i am not able to find Direction.</p>
  
  <p>Also I have implemented Custom Page Control and I am finding current Index from these methods. When These method not called my PageControl is now working find.</p>
  
  <p>I am not able to find any solution for this. </p>