UserDefaults bug

userDefaultsWithoutDelay.swift

// in AppDelegate.swift
let TableViewControllerDidAppear = NSNotification.Name("TableViewController did Appear")
// in PreferencesViewController.swift
class PreferencesViewController: NSViewController {

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do view setup here.
        NotificationCenter.default.addObserver(self, selector: #selector(userDefaultsDidChange), name: UserDefaults.didChangeNotification, object: UserDefaults.standard)
        NotificationCenter.default.addObserver(self, selector: #selector(tableViewDidAppear(noti:)), name: TableViewControllerDidAppear, object: nil)
    }
    
    override func viewWillDisappear() {
        super.viewWillDisappear()
        
        NotificationCenter.default.removeObserver(self, name: UserDefaults.didChangeNotification, object: nil)
        NotificationCenter.default.removeObserver(self, name: TableViewControllerDidAppear, object: nil)
    }
    
    weak var tableViewController:TableViewController?
    
    func userDefaultsDidChange() {
        guard let controller = tableViewController else { return }
        
        controller.run()
    }
    
    func tableViewDidAppear(noti:Notification) {
        if let controller = noti.object as? TableViewController {
            tableViewController = controller
        }
    }
}
// in TableViewController.swift
class TableViewController: NSViewController, NSTableViewDelegate {
    override func viewDidLoad() {
        super.viewDidLoad()
        // Do view setup here.
        run()
        NotificationCenter.default.post(name: TableViewControllerDidAppear, object: self)
    }
    
    func run() {
        // do things
    }
}