I want to create a new UIWindow in Swift project,but something wrong -

i create new project in swift,and want create new uiwindow,here code in controller:

override func viewdidload() {         super.viewdidload()         // additional setup after loading view, typically nib.         let mywindow = uiwindow(frame: uiscreen.mainscreen().bounds)         mywindow.backgroundcolor = uicolor.redcolor()         mywindow.hidden = false       } 

when run project,i got message: 'application windows expected have root view controller @ end of application launch'.but @ objective-c project,it's ok.

who can tell me what's wrong whit project?

thanks.

finally,i got answer myself.you can't create new uiwindow @ time when loading new viewcontroller,but can after view loaded.here code:

    let mywindow = {void->uiwindow in         let cwindow = uiwindow(frame: uiscreen.mainscreen().bounds)         cwindow.backgroundcolor = uicolor.redcolor()         return cwindow     }()      override func touchesbegan(touches: set<uitouch>, withevent event: uievent?) {          mywindow.hidden = false     }