title: UIPageViewController views messed up if user moves too quickly
body: <p>I have a <code>UIPageViewController</code> that uses an integer to tell which page it is on. It works fine, but if the user quickly swipes several times to get to a page further back, the integer changes more quickly than the views do, and then the whole thing falls apart (the app thinks it is on page 7 when it could be displaying page 3). What am I doing wrong? Is there a different method I should use to tell where I am? Thanks.</p>
  
  <pre><code>- (UIViewController *)pageViewController:(UIPageViewController *)pageViewController viewControllerAfterViewController:(UIViewController *)viewController {
      if (pageNumber == 0) {
          pageNumber++;
          NSLog(@"%i", pageNumber);
          Two *two = [[Two alloc] init];
          return two;
      } else if (pageNumber == 1) {
          pageNumber++;
          NSLog(@"%i", pageNumber);
          Three *three = [[Three alloc] init];
          return three;
      } else if (pageNumber &gt;= 2) {
          return nil;
      } else {
          return nil;
      }
  }
  </code></pre>