title: Developing a Walkthrough Screen on Swift3
body: <p>I am quite new in Swift and I am trying to develop a walkthrough screen for my application. I am following a book tutorial, but I get the following error and I can't continue.</p>
  
  <p>I think the problem is in the different update of Swift. Would you please help me how to fix it?</p>
  
  <pre><code>self.pageViewController = (self.storyboard?.instantiateViewController(withIdentifier: "pageViewController") as! UIPageViewController!) as! UIPageViewControllerDataSource!
  
  let startVC = self.viewControllerAtIndex(index: 0) as ContentViewController
  let viewControllers = NSArray(object: startVC)
  
  self.pageViewController.view.frame = CGRectMake (0,30,self.view.frame.width,self.view.frame.height-60)
  
  self.addChildViewController(pageViewController as! UIViewController)
  self.view.addSubview(pageViewController.view)
  
  self.pageViewController.didMoveToParentViewController(self)
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/ldLXk.png" alt="enter image description here"></p>