Custom UIControl element with global state for all instances

Question

I have drawer controller presenting menu in the iOS app. This menu is toggled by pressing menu buttons (UIButton) available on each screen.

As you can see in the mock: menu buttons can have red dot showing that new content is available - for this case I simply have two images for menu button without dot and with it.

I thought about making custom UIControl with "global" property for this dot. Is it the right way?

class MenuButton : UIButton {
  static var showNotificationDot : Bool = false
}

Answer 1

For example you could create subclass UIButton and add observer.

class MyButton: UIButton {

    static let notificationKey = NSNotification.Name(rawValue: "MyButtonNotificationKey")

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.subcribeForChangingState()
    }

    required init?(coder aDecoder: NSCoder) {
        super.init(coder: aDecoder)
    }

    fileprivate func subcribeForChangingState() {
        NotificationCenter.default.addObserver(forName: MyButton.notificationKey, object: nil, queue: nil) { notificaton in
            if let state = notificaton.object as? Bool {
                self.changeState(active: state)
            }
        }
    }

    fileprivate func changeState(active: Bool) {
        //change ui of all instances
        print(active)
    }

    deinit {
        NotificationCenter.default.removeObserver(self)
    }
}

And change UI from any place like this:

NotificationCenter.default.post(name: MyButton.notificationKey, object: true)