Using Channels #2

UsingChannels-NotificationCenter-Definition.swift

enum Theme: String {
    case light, dark
}

class UserSettings {
  
    static let shared = UserSettings(notificationCenter: .default)
    let notificationCenter: NotificationCenter
  
    var theme: Theme = .light {
        didSet {
            let name = ThemeDidChangeNotification.name
            let userInfo = ThemeDidChangeNotification.userInfo(with: theme)
            notificationCenter.post(name: name, object: self, userInfo: userInfo)
        }
    }
  
    init(notificationCenter: NotificationCenter) {
        self.notificationCenter = notificationCenter
    }
}

struct ThemeDidChangeNotification {
  
    static let name = Notification.Name(rawValue: "ThemeDidChangeNotification")
    let theme: Theme
  
    init?(userInfo: [AnyHashable: Any]?) {
        if let rawTheme = userInfo?["theme"] as? String,
           let theme = Theme(rawValue: rawTheme) {
            self.theme = theme
        } else {
            return nil
        }
    }
  
    static func userInfo(with theme: Theme) -> [AnyHashable: Any] {
        return ["theme": theme.rawValue]
    }
}

UsingChannels-NotificationCenter-Usage.swift

class HomeViewController: UIViewController {
  
    private let userSettings = UserSettings.shared
  
    override func viewDidLoad() {
        super.viewDidLoad()
        subscribe()
    }
  
    func subscribe() {
        let notificationCenter = userSettings.notificationCenter
    
        notificationCenter.addObserver(forName: ThemeDidChangeNotification.name, object: userSettings, queue: .main) { (notification) in
            guard let theme = ThemeDidChangeNotification(userInfo: notification.userInfo)?.theme else { return }
            // Apply theme here.
        }
    }
}