How can you use SwiftUI in a Notification Content Extension?

I can't work out how to use SwiftUI in a notification content extension. It always appears black for me when the extension runs.

Here's the code in my extension right now:

class NotificationViewController: UIViewController, UNNotificationContentExtension {

    override func viewDidLoad() {
        super.viewDidLoad()

        let child = UIHostingController(rootView: TaskCell_Previews.previews)
        addChild(child)
        child.view.frame = view.frame
        view.addSubview(child.view)
        child.didMove(toParent: self)

        NSLayoutConstraint.activate([
            child.view.widthAnchor.constraint(equalTo: view.widthAnchor, multiplier: 1),
            child.view.heightAnchor.constraint(equalTo: view.heightAnchor, multiplier: 1),
            child.view.centerXAnchor.constraint(equalTo: view.centerXAnchor),
            child.view.centerYAnchor.constraint(equalTo: view.centerYAnchor)
        ])
    }
    
    func didReceive(_ notification: UNNotification) {

    }

}

In this case, I'm just putting `TaskCell_Previews` in to try to get it working. Whenever I tap on the notification, it just shows a blank view (which has a 1-1 aspect ratio as that's defined in my plist).

Thanks for any help/advice.