Pass data from NSViewController to another NSWindowController

Question

I'd like to have data inputted from one view controller (with its own window controller) be passed along (only one way) to another window controller with its own view controller. The reason I'd like to pass it specifically to the window controller is because I have a toolbar on the window controller. I've used passing data using segues between view controllers, but when I try to pass to a window controller, the data does not update. Here is my prepare(for: sender:) method:

override func prepare(for segue: NSStoryboardSegue, sender: Any?) {
    let windowController = segue.destinationController as! WindowController
    windowController.test = "hello"
}

Where test is a variable in my WindowController class. Also, if there is a better way to do this, or a better approach overall, any help would be greatly appreciated.