title: why is "window.rootViewController = self.navigationController" needed in Xcode 4 Navigation Based App?
body: <p>Why is the following line needed within the didFinishLaunchingWithOptions method?  </p>
  
  <pre><code>self.window.rootViewController = self.navigationController;
  </code></pre>
  
  <p>That is, noting there is already in Interface Builder, in the MainWindow XIB, the navigation controller with it's navigation bar and RootViewController within it's hierarchy.</p>
  
  <p>Copy of whole method for reference is:</p>
  
  <pre><code>- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
      // Override point for customization after application launch.
      // Add the navigation controller's view to the window and display.
      self.window.rootViewController = self.navigationController;
      [self.window makeKeyAndVisible];
      return YES;
  }
  </code></pre>