Our implementation of the Coordinators pattern — V2, more strict than V1

Coordinators-v2.swift

//  Coordinator.swift

import Foundation

public protocol Coordinator: class {
    var components: CoordinatorComponents { get }

    /// Set up here everything that needs to happen just before the Coordinator is presented
    ///
    /// - Parameter modalSetup: A parameter you can use to customize the default mainViewController's
    ///                         presentation style (e.g. `modalPresentationStyle`, etc), and to set the initial
    ///                         ViewController of the Coordinator's UINavigationController (if you didn't
    ///                         already set it in the init() when instantiating CoordinatorComponents).
    ///
    /// - Attention: Don't call this method directly. It will be called automatically when you call
    ///              `present(childCoordinator:animated:completion:)`
    func start(modalSetup: ViewControllerInitialSetup & ViewControllerModalSetup)

    /// ⬆️ Present a child Coordinator modally
    /// - Note: You can pass an overrideModalSetup closure if you need to customize the
    ///         modalPresentationStyle/modalTransitionStyle etc for that modal presentation
    func present(childCoordinator coordinator: Coordinator, animated: Bool,
                 overrideModalSetup: ((ViewControllerModalSetup) -> Void)?, completion: (() -> Void)?)
    /// ⬇️ Dismiss the top modal child Coordinator
    func dismissChildCoordinator(animated: Bool, completion: (() -> Void)?)

    /// ➡️ Push a ViewController on the current coordinator's NavigationController
    func pushViewController(_ viewController: UIViewController, animated: Bool)
    /// ⬅️ Pop the top ViewController from the current coordinator's NavigationController
    func popViewController(animated: Bool)

    /// ⏮ Rewind to the root ViewController of the current coordinator's NavigationController
    func popToRootViewController(animated: Bool)
}

/// Exposes what is allowed to be changed on the mainVC during setup in the `start(modalSetup:)` implementation
public protocol ViewControllerModalSetup: class {
    var definesPresentationContext: Bool { get set }
    var providesPresentationContextTransitionStyle: Bool { get set }
    var modalTransitionStyle: UIModalTransitionStyle { get set }
    var modalPresentationStyle: UIModalPresentationStyle { get set }
    var modalPresentationCapturesStatusBarAppearance: Bool { get set }
    // We might want to add some other stuff later, like transitioningDelegate and stuff, this might not be exhaustive yet
}

public protocol ViewControllerInitialSetup: class {
    func setInitialViewController(_ vc: UIViewController)
}

/**
 Struct used for gathering Coordinator's properties and setting their default value.
 */
public class CoordinatorComponents {
    fileprivate let mainViewController = UINavigationController()
    fileprivate var childCoordinators = [Coordinator]()

    public init() {}
}

// MARK: Default Implementation

extension UINavigationController: ViewControllerInitialSetup, ViewControllerModalSetup {
    public func setInitialViewController(_ vc: UIViewController) {
        self.viewControllers = [vc]
    }
}

public extension Coordinator {
    func present(childCoordinator coordinator: Coordinator, animated: Bool = true, overrideModalSetup: ((ViewControllerModalSetup) -> Void)? = nil, completion: (() -> Void)? = nil) {
        self.components.childCoordinators.append(coordinator)
        coordinator.start(modalSetup: self.components.mainViewController)
        overrideModalSetup?(self.components.mainViewController)
        self.components.mainViewController.present(coordinator.components.mainViewController, animated: animated, completion: completion)
    }
    func dismissChildCoordinator(animated: Bool = true, completion: (() -> Void)? = nil) {
        self.components.mainViewController.dismiss(animated: animated, completion: completion)
        self.components.childCoordinators.removeAll()
    }

    func pushViewController(_ viewController: UIViewController, animated: Bool) {
        self.components.mainViewController.pushViewController(viewController, animated: animated)
    }
    func popViewController(animated: Bool) {
        self.components.mainViewController.popViewController(animated: animated)
    }

    func popToRootViewController(animated: Bool) {
        self.components.mainViewController.popToRootViewController(animated: animated)
    }
}

extension UITabBarController {
    public func configureTabs(using tabsCoordinators: [Coordinator]) {
        tabsCoordinators.forEach { $0.start(modalSetup: $0.components.mainViewController) }
        self.viewControllers = tabsCoordinators.map { $0.components.mainViewController }
    }
}

TutorialCoordinator.swift

protocol TutorialCoordinatorDelegate {
  func dismissTutorial()
}

class TutorialCoordinator: Coordinator {
  let components = CoordinatorComponents()
  weak var delegate: TutorialCoordinatorDelegate?
  
  func start(modalSetup: ViewControllerInitialSetup & ViewControllerModalSetup) {
    let step1VC = TutoStep1ViewController.instantiate()
    modalSetup.setInitialViewController(step1VC)
    modalSetup.modalPresentationStyle = .formSheet
  }
}

extension TutorialCoordinator: TutoStep1ViewControllerNavigation {
  func showTutorialStep2() {
    let step2VC = TutoStep2ViewController.instantiate()
    self.pushViewController(step2VC)
  }
}

extension TutorialCoordinator: TutoStep2ViewControllerNavigation {
  func closeTutorial() {
    self.delegate.dismissTutorial()
  }
}

TutoStep1ViewController.swift

import UIKit

protocol TutoStep1ViewControllerNavigation: class {
  // Add here functions to navigate away from this screen, to ask the Coordinator to show another screen
  func showTutorialStep2()
}

final class TutoStep1ViewController: UIViewController {

  weak var coordinator: TutoStep1ViewControllerNavigation?
  
  // MARK: - Private Properties
  
  // MARK: - Setup
  
  static func instantiate(/* dependencies: Dependencies */) -> TutoStep1ViewController {
    let vc = StoryboardScene.Tutorial.tutoStep1ViewController.instantiate() // Constants generated by SwiftGen
    // vc.dependences = dependencies
    return vc
  }
  
  // MARK: - Internal Funcs

  @IBAction func goNext() {
    self.coordinator?.showTutorialStep2()
  }
}

TutoStep2ViewController.swift

import UIKit

protocol TutoStep2ViewControllerNavigation: class {
  // Add here functions to navigate away from this screen, to ask the Coordinator to show another screen
  func closeTutorial()
}

final class TutoStep2ViewController: UIViewController {

  weak var coordinator: TutoStep2ViewControllerNavigation?
  
  // MARK: - Private Properties
  
  // MARK: - Setup
  
  static func instantiate(/* dependencies: Dependencies */) -> TutoStep2ViewController {
    let vc = StoryboardScene.Tutorial.tutoStep2ViewController.instantiate() // Constants generated by SwiftGen
    // vc.dependences = dependencies
    return vc
  }
  
  // MARK: - Internal Funcs

  @IBAction func close() {
    self.coordinator?.closeTutorial()
  }
}

Hi Olivier, Thanks for sharing this pattern.
I am planning to use Coordinators in my current projet and I have a question :) :

Does the coordinator responsable for the Data (Web services calls for example) ? Or do you use an other dedicated class for this ?
Thanks