How do i use coordinators with a UIITabBarController?

I want to share an example for this question. My approach a little bit different and TabCoordinator not contains everything in his body. Instead of this, every coordinator has relation with its controller and in every UIViewController (in tabbar controller) has its UITabBarController reference like delegation pattern.

class Coordinator {

    var navigationController: UINavigationController?
    var childCoordinators: [Coordinator] = [Coordinator]()

    init(with navigation: UINavigationController) {
        self.navigationController = navigation
    }

    func start() {}

}

Then here is the coordinators.

Home Coordinator

final class HomeCoordinator: Coordinator {

    var currentController: HomeController?
    weak var tabController: TabController?


    override init(with navigation: UINavigationController) {
        super.init(with: navigation)

        currentController = HomeController()
        currentController?.coordinator = self
        childCoordinators.append(self)
    }

    override func start() {

        navigationController?.pushViewController(currentController ?? UIViewController(),
                                                 animated: true)

    }

    public func getHomeData() {

        // GETTING HOME DATA

        tabController?.requestFromHomeController()

    }

}

About Coordinator

final class AboutCoordinator: Coordinator {

    var currentController: AboutController?
    weak var tabController: TabController?

    override init(with navigation: UINavigationController) {
        super.init(with: navigation)

        currentController = AboutController()
        currentController?.coordinator = self
        childCoordinators.append(self)
    }


    override func start() {

        navigationController?.pushViewController(currentController ?? UIViewController(),
                                                 animated: true)

    }

    public func getAboutData() {

        // GETTING ABOUT DATA

        tabController?.requestFromAboutController()

    }
}

UITabBarController

final class TabController: UITabBarController {

    weak var coordinator: MainTabCoordinator?


    override func viewDidLoad() {
        super.viewDidLoad()


        let navigationController1 = UINavigationController()
        let coordinator1 = HomeCoordinator(with: navigationController1)
        coordinator1.tabController = self
        coordinator1.currentController?.tabBarItem = UITabBarItem(title: "HOME",
                                                                  image: nil,
                                                                  tag: 11)

        let navigationController2 = UINavigationController()
        let coordinator2 = AboutCoordinator(with: navigationController2)
        coordinator2.tabController = self
        coordinator2.currentController?.tabBarItem = UITabBarItem(title: "ABOUT",
                                                                  image: nil,
                                                                  tag: 22)


        viewControllers = [
            coordinator1.currentController!,
            coordinator2.currentController!
        ]

        tabBar.barTintColor = UIColor.white
        tabBar.isTranslucent = false

    }

    public func requestFromHomeController() {
        print("Home Triggered the function")

        coordinator?.fetchHome(with: "Simple Data",
                               completion: { (dictionary, error) in
                                print("dict from home -> ", dictionary)
        })



    }

    public func requestFromAboutController() {
        print("About Triggered the function")

        coordinator?.handleAbout(with: "Simple Data",
                                 completion: { (dictionary, error) in
                                    print("dict from about -> ", dictionary)
        })
    }    
}

Prepare the app from AppDelegate

in application(_ application: UIApplication, didFinishLaunchingWithOptions function

let appNavigationController = UINavigationController()
let tabCoordinator = MainTabCoordinator(with: appNavigationController ?? UINavigationController())
tabCoordinator.start()
window?.rootViewController = appNavigationController

Here is the AboutController

final class AboutController: UIViewController{

    weak var coordinator: AboutCoordinator?

    // define a button and add its target to handleButton function

    @objc private func handleButton(_ sender: UIButton) {

        coordinator?.getAboutData()
    }


    override func viewDidLoad() {
        super.viewDidLoad()

        // ui settings
    }
}

MainTabCoordinator

final class MainTabCoordinator: Coordinator {

    var currentController: TabController?


    override init(with navigation: UINavigationController) {
        super.init(with: navigation)

        self.currentController = TabController()
        self.childCoordinators.append(self)
        currentController?.coordinator = self
    }



    override func start() {

        navigationController?.pushViewController(currentController ?? UIViewController(),
                                                 animated: true)

    }

    func fetchHome(with title: String, completion:  @escaping (_ result: Dictionary<String,Any>, _ error: NSError?) -> ()) {

        completion(["ss":"ss"], nil)

    }


    func handleAbout(with title: String, completion: @escaping (_ result: Dictionary<String,Any>, _ error: NSError?) -> ()) {

        completion(["ss":"ss"], nil)
    }

}

The working schema is like that below:

AboutController ---> triggered action ---> AboutCoordinator ---> TabBarController reference has request to about action ----> MainTabCoordinator handle works.

My Coordinator structure is a different than yours, but it might help you. In my case, the Coordinator protocol has a rootViewController property which points to that Coordinator's ViewController.

My AppCoordinator then persists a TabCoordinator, which looks somewhat like this: (In the real code, the persisted coordinators are NavigationCoordinators, which are special Coordinators that hold NavigationControllers. In this example I just added the ViewControllers and removed memory management stuff to make it easier to understand.)

final class TabCoordinator: NSObject, Coordinator {

var rootViewController: UIViewController {
    return tabController
}

let tabController: UITabBarController

let homeCoordinator: HomeCoordinator
let historyCoordinator: HistoryCoordinator
let profileCoordinator: ProfileCoordinator

var coordinators: [Coordinator] {
    return [homeCoordinator, historyCoordinator, profileCoordinator]
}

init(client: HTTPClient, persistence: Persistence) {

    tabController = UITabBarController()

    homeCoordinator = HomeCoordinator(client: client, persistence: persistence)

    historyCoordinator = HistoryCoordinator(client: client, persistence: persistence)

    profileCoordinator = ProfileCoordinator(client: client, persistence: persistence)

    var controllers: [UIViewController] = []

    let homeViewController = homeCoordinator.rootViewController
    homeViewController.tabBarItem = UITabBarItem(title: Localization.homeTab.string, image: Asset.iconMenuRecharge.image, selectedImage: Asset.iconMenuRechargeActivated.image)

    let historyViewController = historyCoordinator.rootViewController
    historyViewController.tabBarItem = UITabBarItem(title: Localization.walletTab.string, image: Asset.iconMenuWallet.image, selectedImage: Asset.iconMenuWalletActivated.image)

    let profileViewController = profileCoordinator.rootViewController
    profileViewController.tabBarItem = UITabBarItem(title: Localization.profileTab.string, image: Asset.iconMenuProfile.image, selectedImage: Asset.iconMenuProfileActivated.image)

    super.init()

    controllers.append(homeViewController)
    controllers.append(historyViewController)
    controllers.append(profileViewController)

    tabController.viewControllers = controllers
    tabController.tabBar.isTranslucent = false
    tabController.delegate = self

}
}

So basically, your TabBarController is a TabCoordinator whose's rootViewController is a TabBarController. The TabCoordinator instantiates the relevant Coordinators and add their respective rootViewControllers to the tab.

Here's a basic implementation of the NavigationCoordinator:

class NavigationCoordinator: NSObject, Coordinator {    

    public var navigationController: UINavigationController     

    public override init() {
        self.navigationController = UINavigationController()
        self.navigationController.view.backgroundColor = .white
        super.init()
    }    

    public var rootViewController: UIViewController {
        return navigationController
    }
}

And a basic version of a Coordinator:

public protocol Coordinator: class {    
    var rootViewController: UIViewController { get }    
}