osx - NSWindow returns nil (NSApplication) -

i've come across issue cannot access app's main window, returns nil.

let window = nsapplication.sharedapplication().mainwindow 

i've found similar questions:

how main window (app delegate) other class (subclass of nsviewcontroller)?

but doing:

let window = (nsapplication.sharedapplication() as! nsarray).objectatindex(0) 

doesn't seem work either.

do have mess around in storyboard?

thanks in advance.

update:

i'm trying port objective-c.

    nswindow *mainwindow = [[[nsapplication sharedapplication] windows] objectatindex:0];     nslog(@"%@", mainwindow.contentviewcontroller); 

this returns proper value, when put in viewdidload() block in nsviewcontroller, i'm guessing there wrong nsapplication.sharedapplication().

it can return nil if main app window not active on macos. instance ran when making drag , drop file uploader. if window not in front (on operating system) return nil. following line of code activate app (bring front)

nsapp.activateignoringotherapps(true) 

i needed timer delay call of mainwindow in case.