Coordinators and memory management

A talk given at Cocoaheads Lille in April 2018.

1. Coordinators and memory
2. We all have this ViewController → Layout → View State management → Data fetching & persistance → Navigation
3. Why is this? → ViewController have an unclear role in UIKit → Apple's vision of MVC is not matching our needs
4. What is MVC?
5. What are Apple's components of MVC?
6. Why does this not match our expectations? → Apple expects us to do a local first app with CoreData → In this context their architecture makes perfect sense
7. MVVM to the rescue
8. MVVM to the rescue → The ViewController becomes just a part of the view level
9. Remember our ViewController? → Layout: UIView → View State management: UIViewController → Data fetching & persistance: ViewModel → Navigation: ????
11. EXAMPLE CASE
13. Introducing Coordinator
14. What does a Coordinator do? → Manages the navigation flow → Instanciates the controllers and injects dependencies
15. How does it do it? → It's a plain Swift object → You do what you want with it → You just implement the Coordinator Protocol → You use delegation (or Reactive Programming) at the controller level
16. Anatomy of a Coordinator public protocol Coordinator { func start(animated: Bool) }
17. class AppCoordinator { let window: UIWindow let navigationController: UINavigationController! let homeController: HomeViewController! init(window: UIWindow) { self.window = window } } extension AppCoordinator: Coordinator { func start(animated: Bool) { homeController = HomeViewController.instanciateFromStoryboard() navigationController = UINavigationController(root: homeController) window.rootViewController = navigationController window.makeKeyAndVisible() } }
18. class AppDelegate: UIResponder, UIApplicationDelegate { var window: UIWindow? var coordinator: Coordinator! func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]? ) -> Bool { let window = UIWindow(frame: UIScreen.main.bounds) coordinator = AppCoordinator(window: window) coordinator.start(animated: false) self.window = window } }
19. class DetailCoordinator { let navigationController: UINavigationController let detailController: DetailViewController init(_ navigationController: UINavigationController) { self.navigationController = navigationController } } extension DetailCoordinator: Coordinator { func start(animated: Bool) { let detailController = DetailViewController.instanciateFromStoryboard() navigationController.pushViewController(detailController, animated: animated) } }
20. class AppCoordinator { let window: UIWindow let navigationController: UINavigationController! let homeController: HomeViewController! var childCoordinator: Coordinator? init(window: UIWindow) { self.window = window } } extension AppCoordinator: Coordinator { func start(animated: Bool) { homeController = HomeViewController.instanciateFromStoryboard() homeController.delegate = self navigationController = UINavigationController(root: homeController) window.rootViewController = navigationController window.makeKeyAndVisible() } } extension AppCoordinator: HomeControllerDelegate { func didTouchDetailButton() { let coordinator = DetailCoordinator(_ navigationController: navigationController) coordinator.start() childCoordinator = coordinator } }
21. Yay we did it!
23. Wait what?! Beware the zombie Coordinators and UIViewControllers
25. What's the problem here ? → UIKit creates a strong reference → But Coordinator should own it... → UIKit decides when the view is released
26. Play fair with UIKit → Don't fight it, embrace it → UIKit will always be there
30. ! How do I let the parent Coordinator know that the Coordinator is not needed anymore?
32. The lifecycle probe → When the ViewController is deallocated it sends a message to the Coordinator → The Coordinator sends a message to its parent to be released
33. SO MUCH WORK
34. Meet Yui Github: CallMeSH/Yui
35. Yui streamlines the process → Conform to the protocol → Follow the guidelines → You're done !
36. DEMO Time
37. Thank You Github: CallMeSH/Yui Twitter: @CallMeSH LinkedIn: Charles-Henri DUMALIN