Lightweight routing on microservices

Mobile applications have become really big lately - not only in the sense of their importance to you and me, but also in the literal sense.

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MVVM , ( ). OrdersVC, - — OrdersVM. , :

, , - :

final class OrderDetailsVM: IPerRequest {
    typealias Arguments = Order

    let title: String

    required init(container: IContainer, args: Order) {
        self.title = "Details of \(args.name) #\(args.id)"
    }
}

IPerRequest ( — DI), , DI-. , . :

final class OrderDetailsVC: UIViewController, IHaveViewModel {
    typealias ViewModel = OrderDetailsVM

    private lazy var titleLabel = UILabel()

    override func viewDidLoad() {
        super.viewDidLoad()

        view.backgroundColor = .white
        view.addSubview(titleLabel)
        titleLabel.translatesAutoresizingMaskIntoConstraints = false
        titleLabel.centerXAnchor
            .constraint(equalTo: view.centerXAnchor)
            .isActive = true
        titleLabel.topAnchor
            .constraint(equalTo: view.topAnchor, constant: 24)
            .isActive = true
    }

    func viewModelChanged(_ viewModel: OrderDetailsVM) {
        titleLabel.text = viewModel.title
    }
}

OrderDetailsVC IHaveViewModel ( — MVVM) , -. .

OrdersVC , :

extension OrdersVC: UITableViewDelegate {
    func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        viewModel?.showOrderDetails(forOrderIndex: indexPath.row)
    }
}

, , MVC, iOS, MVVM . ( ) , iOS - . , , .

, OrdersVM, , :

final class OrdersVM: IPerRequest, INotifyOnChanged {
    typealias Arguments = Void

    var orders: [OrderVM] = []
    private let ordersProvider: OrdersProvider

    required init(container: IContainer, args: Void) {
        self.ordersProvider = container.resolve()
    }

    func loadOrders() {
        ordersProvider.loadOrders() { [weak self] model in
            self?.orders = model.map { OrderVM(order: $0) }
            self?.changed.raise()
        }
    }

    func showOrderDetails(forOrderIndex index: Int) {
        let order = orders[index].order
        //   ?
        // ...
    }
}

IPerRequest, , . OrdersProvider, . orders, - changed.raise().

showOrderDetails(forOrderIndex:) , . iOS, present(_:animated:completion:), .

MVC , MVVM : - . , - , - - .  — , .

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, , OrdersVM , OrdersProvider.

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, , , , present(_:animated:completion:). , :

1.  — . , VC - , -.
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4.  — . , .

, . , , PresenterService.

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:

1. UIViewController, .
2. - - .
3. .

, :

final class PresenterService: ISingleton {

    private unowned let container: IContainer

    public required init(container: IContainer, args: Void) {
        self.container = container
    }
}

, . , , - - , : , , ,  — . , PresenterService ,  — .

 —  — :

var topViewController: UIViewController? {
   let keyWindow = UIApplication.shared.windows.first { $0.isKeyWindow }
   return findTopViewController(in: keyWindow?.rootViewController)
}

func findTopViewController(in controller: UIViewController?) -> UIViewController? {
   if let navigationController = controller as? UINavigationController {
       return findTopViewController(in: navigationController.topViewController)
   } else if let tabController = controller as? UITabBarController,
       let selected = tabController.selectedViewController {
       return findTopViewController(in: selected)
   } else if let presented = controller?.presentedViewController {
       return findTopViewController(in: presented)
   }
   return controller
}

findTopViewController(in:) , , , . , , , , , , .

, . , - , . , , , , :

func present<VC: UIViewController & IHaveViewModel>(
    _ viewController: VC.Type,
    args: VC.ViewModel.Arguments) where VC.ViewModel: IResolvable {

    let vc = VC()
    vc.viewModel = container.resolve(args: args) //   
    topViewController?.present(vc, animated: true, completion: nil)
}

. MVVM DI- , , .

1. , , , .
2. - . - , IResolvable ( DI). , . - , - viewModel IHaveViewModel ( MVVM). , VC.ViewModel.Arguments . - DI- . : DI-, MVVM , — . !
3. , , , , - , present(_:animated:completion:).

, PresenterService, :

final class PresenterService: ISingleton {

    private unowned let container: IContainer

    private var topViewController: UIViewController? {
        let keyWindow = UIApplication.shared.windows.first { $0.isKeyWindow }
        return findTopViewController(in: keyWindow?.rootViewController)
    }

    required init(container: IContainer, args: Void) {
        self.container = container
    }

    func present<VC: UIViewController & IHaveViewModel>(
        _ viewController: VC.Type,
        args: VC.ViewModel.Arguments) where VC.ViewModel: IResolvable {

        let vc = VC()
        vc.viewModel = container.resolve(args: args)
        topViewController?.present(vc, animated: true, completion: nil)
    }

    func dismiss() {
        topViewController?.dismiss(animated: true, completion: nil)
    }

    private func findTopViewController(
        in controller: UIViewController?) -> UIViewController? {

        if let navigationController = controller as? UINavigationController {
            return findTopViewController(in: navigationController.topViewController)
        } else if let tabController = controller as? UITabBarController,
            let selected = tabController.selectedViewController {
            return findTopViewController(in: selected)
        } else if let presented = controller?.presentedViewController {
            return findTopViewController(in: presented)
        }
        return controller
    }
}

, , — dismiss(), . OrdersVM, PresenterService , :

final class OrdersVM: IPerRequest, INotifyOnChanged {
    typealias Arguments = Void

    var orders: [OrderVM] = []

    private let ordersProvider: OrdersProvider
    private let presenter: PresenterService

    required init(container: IContainer, args: Void) {
        self.ordersProvider = container.resolve()
        self.presenter = container.resolve()
    }

    func loadOrders() {
        ordersProvider.loadOrders() { [weak self] model in
            self?.orders = model.map { OrderVM(order: $0) }
            self?.changed.raise()
        }
    }

    func showOrderDetails(forOrderIndex index: Int) {
        let order = orders[index].order
        //     
        presenter.present(OrderDetailsVC.self, args: order)
    }
}

, PresenterService showOrderDetails(forOrderIndex:).

, . ?

UINavigationController . , , NavigationService. , , :

1. UINavigationController, .
2. - - .
3. .

, PresenterService, , . , .

final class NavigationService: ISingleton {

    private unowned let container: IContainer

    private var topNavigationController: UINavigationController? {
        let keyWindow = UIApplication.shared.windows.first { $0.isKeyWindow }
        let root = keyWindow?.rootViewController
        let topViewController = findTopViewController(in: root)
        return findNavigationController(in: topViewController)
    }

    required init(container: IContainer, args: Void) {
        self.container = container
    }

    func pushViewController<VC: UIViewController & IHaveViewModel>(
        _ viewController: VC.Type,
        args: VC.ViewModel.Arguments) where VC.ViewModel: IResolvable {

        let vc = VC()
        vc.viewModel = container.resolve(args: args)
        topNavigationController?.pushViewController(vc, animated: true)
    }

    func popViewController() {
        topNavigationController?.popViewController(animated: true)
    }

    private func findTopViewController(
        in controller: UIViewController?) -> UIViewController? {

        if let navigationController = controller as? UINavigationController {
            return findTopViewController(in: navigationController.topViewController)
        } else if let tabController = controller as? UITabBarController,
            let selected = tabController.selectedViewController {
            return findTopViewController(in: selected)
        } else if let presented = controller?.presentedViewController {
            return findTopViewController(in: presented)
        }
        return controller
    }

    private func findNavigationController(
        in controller: UIViewController?) -> UINavigationController? {

        if let navigationController = controller as? UINavigationController {
            return navigationController
        } else if let navigationController = controller?.navigationController {
            return navigationController
        } else {
            for child in controller?.children ?? [] {
                if let navigationController = findNavigationController(in: child) {
                    return navigationController
                }
            }
        }
        return nil
    }
}

, NavigationService PresenterService, ,  — UITabBarController, . .

. ?

 — , , . MVVM, , DI- — . , :

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PresenterService, , — , MVVM . PresenterService MVVM DI-, , .

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