title: Why does not it display UITableView anymore when embed UINavigationController
body: <p>I am new to iOS development. I am learning Swift now. I currently have a problem that my tableView does not display anything anymore after I add a navigation view controller. I don't understand why. Please help me experts!!</p>
  
  <pre><code>class AppDelegate: UIResponder, UIApplicationDelegate {
  
  var window: UIWindow?
  
  
  func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -&gt; Bool {
      // Override point for customization after application launch.
  
      let mainVC = ViewController()
      let navigationVC = UINavigationController(rootViewController: mainVC)
      window?.rootViewController = navigationVC;
      window?.makeKeyAndVisible()
      return true
  }
  </code></pre>
  
  <p>Code in ViewController:</p>
  
  <pre><code>class ViewController: UIViewController, UITableViewDelegate, UITableViewDataSource {
  @IBOutlet var myTable: UITableView!
  var items: [String] = ["Date Picker","List of Data","Slider","Show Image", "Web Display"];
  
  override func viewDidLoad() {
      super.viewDidLoad()
  
      NSLog("Hello World at console");
      var nib = UINib(nibName: "ListCell", bundle: nil)
      myTable?.registerNib(nib, forCellReuseIdentifier: "ListCell")
      // Do any additional setup after loading the view, typically from a nib.
  }
  </code></pre>