Populating a NSImageView inside NSTouchBar

I'm currently creating a tiny open source app to preview an inside the new Touch Bar. I have a window with a drag n drop view to receive images via it's URL. And a IB Touch Bar with a NSImageView inside a TouchBarView.
interface builder structure (screenshot)

This is working in my MainViewController to show the image in the window:

extension ViewController: DropDestinationViewDelegate {

    func processImageURLs(_ urls: [URL]) {
        for (_,url) in urls.enumerated() {

            // pass URL to Window Controller
            let windowController = WindowController()
            windowController.showImageInTouchBar(url)

            // create the image from the content URL
            if let image = NSImage(contentsOf:url) {

                imagePreviewView.image = image
            }
        }
    }

}

As you can see I use a delegate to listen to the drag n drop events to get the image URL. Now I want to use the image/URL to show the same image inside the Touch Bar. I've created the Touch Bar with Interface Builder and I'm passing the image-url to the WindowController.

In my WindowController I try to handle the image like this:

class WindowController: NSWindowController {

    @IBOutlet var touchBarImageView: NSImageView!

    override func windowDidLoad() {
        super.windowDidLoad()
    }

    func showImageInTouchBar(_ url: URL) {
        print(url)

        if let touchbarImage = NSImage(contentsOf:url) {
            touchBarImageView.image = touchbarImage
        }
    }
}

I'm receiving the correct URL with print(url), but when I try to create the image again, the app is crashing with the following message:

fatal error: unexpectedly found nil while unwrapping an Optional value

I created a pull request with a fix.

Your problem was that you was creating a new WindowController and using this as reference instead using the controller created and used by NSWindow.

Result: