Coordinators Essential tutorial
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README.md

ApplicationCoordinator

A lot of developers need to change navigation flow frequently, because it depends on business tasks. And they spend a huge amount of time for re-writing code. In this approach, I demonstrate our implementation of Coordinators, the creation of a protocol-oriented, testable architecture written on pure Swift without the downcast and, also to avoid the violation of the S.O.L.I.D. principles.

Based on the post about Application Coordinators khanlou.com and Application Controller pattern description martinfowler.com.

Coordinators Essential tutorial. Part I medium.com

Coordinators Essential tutorial. Part II medium.com

Example provides very basic structure with 6 controllers and 5 coordinators with mock data and logic.

I used a protocol for coordinators in this example:

protocol Coordinator: class {
    func start()
    func start(with option: DeepLinkOption?)
}

All flow controllers have a protocols (we need to configure blocks and handle callbacks in coordinators):

protocol ItemsListView: BaseView {
    var authNeed: (() -> ())? { get set }
    var onItemSelect: (ItemList -> ())? { get set }
    var onCreateButtonTap: (() -> ())? { get set }
}

In this example I use factories for creating coordinators and controllers (we can mock them in tests).

protocol CoordinatorFactory {
    func makeItemCoordinator(navController navController: UINavigationController?) -> Coordinator
    func makeItemCoordinator() -> Coordinator
    
    func makeItemCreationCoordinatorBox(navController: UINavigationController?) ->
        (configurator: Coordinator & ItemCreateCoordinatorOutput,
        toPresent: Presentable?)
}

The base coordinator stores dependencies of child coordinators

class BaseCoordinator: Coordinator {
    
    var childCoordinators: [Coordinator] = []

    func start() { }
    func start(with option: DeepLinkOption?) { }
    
    // add only unique object
    func addDependency(_ coordinator: Coordinator) {
        
        for element in childCoordinators {
            if element === coordinator { return }
        }
        childCoordinators.append(coordinator)
    }
    
    func removeDependency(_ coordinator: Coordinator?) {
        guard
            childCoordinators.isEmpty == false,
            let coordinator = coordinator
            else { return }
        
        for (index, element) in childCoordinators.enumerated() {
            if element === coordinator {
                childCoordinators.remove(at: index)
                break
            }
        }
    }
}

AppDelegate store lazy reference for the Application Coordinator

var rootController: UINavigationController {
    return self.window!.rootViewController as! UINavigationController
  }
  
  private lazy var applicationCoordinator: Coordinator = self.makeCoordinator()
  
  func application(_ application: UIApplication,
                   didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    let notification = launchOptions?[.remoteNotification] as? [String: AnyObject]
    let deepLink = DeepLinkOption.build(with: notification)
    applicationCoordinator.start(with: deepLink)
    return true
  }
  
  private func makeCoordinator() -> Coordinator {
      return ApplicationCoordinator(
        router: RouterImp(rootController: self.rootController),
        coordinatorFactory: CoordinatorFactoryImp()
      )
  }