title: How to update UI at main queue in Swift?
body: <p>I want to create a splash screen application that I also have a Class named EXClass.<br>
  for some reasons the EXClass must initialize in main thread and update some UI. <br>
  please reference following swift code.</p>
  
  <pre><code>func applicationDidFinishLaunching(aNotification: NSNotification) {
  
      self.windowController = ......
      self.windowController.showWindow(self)
  
      // In order to show window at the very first time, I create a main queue
      dispatch_async(dispatch_get_main_queue()) {
          self.ex = EXClass()  // this class must init in main thread
      }
  }
  </code></pre>
  
  <p>If I init EXClass in dispatch_async(dispatch_get_main_queue()) that init class is ok but update UI is no effect. why?</p>