title: Control a NSTabViewController from parent View
body: <p>(I'm using storyboards and swift.)</p>
  
  <p>I currently have a NSWindowController which has a NSTabViewController as contentViewController.
  I am now trying to change the Tabs from the NSWindowController via code using </p>
  
  <pre><code>let tabController = self.contentViewController as! NSTabViewController
  tabController.tabView.selectTabViewItemAtIndex(1)
  </code></pre>
  
  <p>but the TabView doesn't change the view.</p>
  
  <p>Am I using the API wrong?</p>