MVVM: "ViewModel" for AppDelegate

Question

My Swift project uses MVVM and I'm wondering what's a way of having a "ViewModel" for my AppDelegate, that could be accessed by all the other ViewControllers. I understand that the AppDelegate isn't really a ViewController to have its own ViewModel, if strictly following MVVM model all throughout the app.

I want to have a state for my whole app for when the user is logged out, downloading something, etc. Perhaps someday the "ViewModel" would have plenty more use.

Should I just have global variables for these statuses or is there a way I can have my AppDelegate have a viewModel property, then let my ViewControllers access it? It just seems "less clean" for me having global objects that aren't constants (that's only what I feel).

I'm also using ReactiveCocoa 4, if that would be of any help.

score 1 · Answer 1 · answered Dec 09 '15 at 19:53

1

While allowing the AppDelegate to be a catch all is a common pitfall to avoid I don't think a ViewModel for the AppDelegate is the best solution. An alternative solution would be to create a "manager" class (or struct) using a singleton that could store login state for the app. That way your login state would be accessible to the rest of the app without adding clutter to the AppDelegate.

answered Dec 09 '15 at 19:53

Christopher Mann

201
1
2

I appreciate your answer and I've thought about the singleton. However, there are so much comments about the singleton that just make me avoid using it... http://stackoverflow.com/questions/137975/what-is-so-bad-about-singletons – ton Dec 10 '15 at 02:22

score 0 · Answer 2 · answered Mar 02 '17 at 23:17

Dependency injection would be the best approach, you can have a class that manages the App's routing and passes the shared objects down the hierarchy.

class ApplicationNavigator {
   let loginManager = LoginManager()

   init(window: UIWindow) {
       let exampleViewModel = ExampleViewModel()
       let exampleViewController = ExampleViewController(loginManager: LoginManager, viewModel: exampleViewModel)

       let navigationController = UINavigationController(rootViewController: exampleViewController)
       window.rootViewController = navigationController
       window.makeKeyAndVisible()
   }
}

Then in the AppDelegate didFinishLaunchingWithOptions

var navigator: ApplicationNavigator?

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    window = UIWindow(frame: UIScreen.main.bounds)
    navigator = ApplicationNavigator(window: window!)
    return true
}

MVVM: "ViewModel" for AppDelegate

2 Answers2