I am attempting to set an outlet for the main window of my app in my App Delegate, then connect it within Interface Builder. I create the outlet within my App Delegate easil
I dont know if this is correct way of doing, but this will solve your problem.
Decalre a NSWindow property in AppDelegate
weak var window: NSWindow!
and set the property in something like windowWillLoad of the NSWindowController
(NSApplication.sharedApplication().delegate as! AppDelegate).window = self.window
You will have to subclass NSWindowController to define windowWillLoad