I am using Xcode 5 in a newly created app and when I just create it I go for the run button e click on it, then the project gets built but it does not show in the iOS Simula
This warning is also reported if you have some code like:
window = UIWindow(frame: UIScreen.mainScreen().bounds)
window?.rootViewController = myAwesomeRootViewController
window?.makeKeyAndVisible()
In this case, go to the first page of target settings and set Main Interface to empty, since you don't need a storyboard entry for your app.