RouteComposer

RouteComposer is the protocol oriented, Cocoa UI abstractions based library that helps to handle view controllers composition, navigation and deep linking tasks in the iOS application.

Can be used as the universal replacement for the Coordinator pattern.

Table of contents

• Navigation concerns
• Installation
• Example
• Requirements
• Testimonials
• Usage
  • Implementation
    • Factory
    • Finder
    • Action
    • Routing Interceptor
    • Context Task
    • Post Routing Task
  • Configuring Step
  • Navigation
  • Deep-linking
  • Troubleshooting
• SwiftUI
• Advanced Configuration
• Contributing
• License
• Articles
• Author

Navigation concerns

There are 2 ways of implementing the navigation available in the iOS application:

• Built-in mechanism provided by Apple using storyboards and segues
• Programmatic navigation directly in the code

The downsides of these two solutions:

• Built-in mechanism: navigation in the storyboards is relatively static and often requires the extra navigation code in the UIViewControllers and can lead to a lot of boilerplate code
• Programmatic navigation: forces UIViewControllers coupling or can be complex depending on the chosen design pattern (Router, Coordinator)

RouteComposer helps

• Facilitate the cutting of an application into small logical steps of navigation
• Provide the navigation configuration in a declarative way and address the majority of the navigation cases
• Remove navigation code from UIViewControllers
• Allow the composition of the UIViewControllers in different ways according to the application state
• Make every UIViewController deep-linkable out of the box
• Simplify the creation of the User facing A/B tests with the different navigation and layout patterns
• Able to work side-by-side with any other navigation mechanism that exist in the IOs application: Builtin or custom

Installation

RouteComposer is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'RouteComposer'

For XCode 10.1 / Swift 4.2 Support

pod 'RouteComposer', '~> 1.4'

And then run pod install.

Once successfully integrated, just add the following statement to any Swift file where you want to use RouteComposer:

import RouteComposer

Check out the Example app included, as it covers most of the general use cases.

Example

To run the example project, clone the repo, and run pod install from the Example directory first.

Requirements

There are no actual requirements to use this library. But if you are going to implement your custom containers and actions you should be familiar with the library concepts and UIKit's view controller navigation stack intricacies.

API documentation

Detailed API documentation can be found here. Test coverage - here

Testimonials

Viz.ai

At Viz.ai, the leading synchronised stroke care service, we went into replacing our entire navigation system, and we knew we needed to address complex and dynamic navigation scenarios. Coordinators and other flow-control libraries just didn't answer our needs, and lead to mixing application logic and navigation, or creating massive coordinator classes. RouteComposer was an amazing fit for us, and actually, as the creator of this library states, it is the drop in replacement for any coordinator code you currently use.

The separation of concerns on this library is absolutely beautiful, and as with anything genius, it all works like magic. It does have a small learning curve, but one that pays off far more than coordinators and flow controllers, and will save you a ton of coding once you implement it.

It makes navigation in the app as simple as saying "go to x with y" and not worrying about the current state or stack. I wholeheartedly recommend it.

Elazar Yifrach, Sr iOS Developer @ Viz.ai

Usage

RouteComposer uses 3 main entities (Factory, Finder, Action) that should be defined by a host application to support it. It also provides 3 helping entities (RoutingInterceptor, ContextTask, PostRoutingTask) that you may implement to handle some default actions during the routing process. There are 2 associatedtype in the description of each entity below:

• ViewController - Type of view controller. UINavigationController, CustomViewController, etc.
• Context - Type of context object that is passed to the router from the hosting application that router will pass to the view controllers it is going to build. String, UUID, Any, etc. Can be optional.

NB

Context represents a payload that you need to pass to your UIViewController and something that distinguishes it from others. It is not a View Model or some kind of Presenter. It is the missing piece of information. If your view controller requires a productID to display its content, and the productID is a UUID, then the type of Context is the UUID. The internal logic belongs to the view controller. Context answers the questions What to I need to present a ProductViewController and Am I already presenting a ProductViewController for this product.

Implementation

1. Factory

Factory is responsible for building view controllers, that the router has to navigate to upon request. Every Factory instance must implement the Factory protocol:

public protocol Factory {

    associatedtype ViewController: UIViewController

    associatedtype Context

    func build(with context: Context) throws -> ViewController

}

The most important function here is build which should actually create the view controller. For detailed information see the documentation. The prepare function provides you with a way of doing something before the routing actually takes place. For example, you could throw from inside this function in order to inform the router that you do not have the data required to display the view correctly. It may be useful if you are implementing Universal Links in your application and the routing can't be handled, in which case the application might open the provided URL in Safari instead.

Example: Basic implementation of the factory for some custom ProductViewController view controller might look like:

class ProductViewControllerFactory: Factory {

    func build(with productID: UUID) throws -> ProductViewController {
        let productViewController = ProductViewController(nibName: "ProductViewController", bundle: nil)
        productViewController.productID = productID // Parameter initialisation can be handled by a ContextAction, see below:

        return productViewController
    }

}

Important note: Automatic associatedtype resolution is broken in XCode 10.2, you must set associated types manually using typealias keyword. Swift compiler bug reported.

2. Finder

Finder helps router to find out if a particular view controller is already present in view controller stack. All the finder instances should conform to Finder protocol.

public protocol Finder {

    associatedtype ViewController: UIViewController

    associatedtype Context

    func findViewController(with context: Context) throws -> ViewController?

}

In some cases, you may use default finders provided by the library. In other cases, when you can have more than one view controller of the same type in the stack, you may implement your own finder. There is an implementation of this protocol included called StackIteratingFinder that helps to solve iterations in view controller stack and handles it. You just have to implement the function isTarget to determine if it's the view controller that you are looking for or not.

Example of ProductViewControllerFinder that can help the router find a ProductViewController that presents a particular product in your view controller stack:

class ProductViewControllerFinder: StackIteratingFinder {

    let iterator: StackIterator = DefaultStackIterator()

    func isTarget(_ productViewController: ProductViewController, with productID: UUID) -> Bool {
        return productViewController.productID == productID
    }

}

SearchOptions is an enum that informs StackIteratingFinder how to iterate through the stack when searching. See documentation.

3. Action

The Action instance explains to the router how the view controller is created by a Factory should be integrated into a view controller stack. Most likely, you will not need to implement your own actions because the library provides actions for most of the default actions that can be done in UIKit like (GeneralAction.presentModally, UITabBarController.add, UINavigationController.push etc.). You may need to implement your own actions if you are doing something unusual.

Check example app to see a custom action implementation.

Example: As you most likely will not need to implement your own actions, let's look at the implementation of PresentModally provided by the library:

class PresentModally: Action {

    func perform(viewController: UIViewController, on existingController: UIViewController, animated: Bool, completion: @escaping (_: RoutingResult) -> Void) {
        existingController.present(viewController, animated: animated, completion: {
            completion(.success)
        })
    }

}

4. Routing Interceptor

Routing interceptor will be used by the router before it will start routing to the target view controller. For example, to navigate to some particular view controller, the user might need to be logged in. You may create a class that implements the RoutingInterceptor protocol and if the user is not logged in, it will present a login view controller where the user can log in. If this process finishes successfully, the interceptor should inform the router and it will continue routing or otherwise stop routing. See example app for details.

Example: If the user is logged in, router can continue routing. If the user is not logged in, the router should not continue

class LoginInterceptor<C>: RoutingInterceptor {

    func perform(with context: C, completion: @escaping (_: RoutingResult) -> Void) {
        guard !LoginManager.sharedInstance.isUserLoggedIn else {
            completion(.failure("User has not been logged in."))
            return
            // Or present the LoginViewController. See Example app for more information. 
        }
        completion(.success)
    }

}

5. Context Task

If you are using one default Factory and Finder implementation provided by the library, you still need to set data in context to your view controller. You have to do this even if it already exists in the stack, if it's just going to be created by a Factory or do any other actions at the moment when router found/created a view controller. Just implement ContextTask protocol.

Example: Even if ProductViewController is present on the screen or it is going to be created you have to set productID to present a product.

class ProductViewControllerContextTask: ContextTask {

    func perform(on productViewController: ProductViewController, with productID: UUID) {
        productViewController.productID = productID
    }

}

See example app for the details.

Or use ContextSettingTask provided with the library to avoid extra code.

6. Post Routing Task

A post-routing task will be called by the router after it successfully finishes navigating to the target view controller. You should implement PostRoutingTask protocol and create all necessary actions there.

Example: You need to log an event in your analytics every time the user lands on a product view controller:

class ProductViewControllerPostTask: PostRoutingTask {

    let analyticsManager: AnalyticsManager

    init(analyticsManager: AnalyticsManager) {
        self.analyticsManager = analyticsManager
    }

    func perform(on productViewController: ProductViewController, with productID: UUID, routingStack: [UIViewController]) {
        analyticsManager.trackProductView(productID: productViewController.productID)
    }

}

Configuring Step

Everything that the router does is configured using a DestinationStep instance. There is no need to create your own implementation of this protocol. Use StepAssembly provided by the library to configure any step that the router should execute during the routing.

Example: A ProductViewController configuration that explains to the router that it should be boxed in UINavigationController which should be presented modally from any currently visible view controller.

let productScreen = StepAssembly(finder: ProductViewControllerFinder(), factory: ProductViewControllerFactory())
        .add(LoginInterceptor<UUID>()) // Have to specify the context type till https://bugs.swift.org/browse/SR-8719, https://bugs.swift.org/browse/SR-8705 are fixed
        .add(ProductViewControllerContextTask())
        .add(ProductViewControllerPostTask(analyticsManager: AnalyticsManager.sharedInstance))
        .using(UINavigationController.push())
        .from(NavigationControllerStep())
        .using(GeneralActions.presentModally())
        .from(GeneralStep.current())
        .assemble()

This configuration means:

• Use ProductViewControllerFinder to potentially find an existing product view controller in the stack, or create it using ProductViewControllerFactory if it has not been found.
• If it was created push it into a navigation stack
• Navigation stack should be provided from another step NavigationControllerStep, that will create a UINavigationController instance
• The UINavigationController instance should be presented modally from any currently visible view controller.
• Before routing run LoginInterceptor
• After view controller been created or found, run ProductViewControllerContextTask
• After successful routing run ProductViewControllerPostTask

See example app to find out different ways to provide and store routing step configurations.

See advanced ProductViewController configuration here.

Navigation

After you have implemented all necessary classes and configured a routing step, you can start to use the Router to navigate. The library provides a DefaultRouter which is an implementation of the Router protocol to handle routing based on the configuration explained above.

Example: The user taps on a cell in a UITableView. It then asks the router to navigate the user to ProductViewController. The user should be logged into see the product details.

struct Configuration {

    static let productScreen = StepAssembly(finder: ProductViewControllerFinder(), factory: ProductViewControllerFactory())
                .add(LoginInterceptor<UUID>())
                .add(ProductViewControllerContextTask())
                .add(ProductViewControllerPostTask(analyticsManager: AnalyticsManager.sharedInstance))
                .using(UINavigationController.push())
                .from(NavigationControllerStep())
                .using(GeneralActions.presentModally())
                .from(GeneralStep.current())
                .assemble()

}

class ProductArrayViewController: UITableViewController {

    let products: [UUID]?

    let router = DefaultRouter()

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        guard let productID = products[indexPath.row] else {
            return
        }
        try? router.navigate(to: Configuration.productScreen, with: productID)
    }

}

Example below shows the same process without the use of RouteComposer

class ProductArrayViewController: UITableViewController {

    let products: [UUID]?

    let analyticsManager = AnalyticsManager.sharedInstance

    override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
        guard let productID = products[indexPath.row] else {
            return
        }

        // Handled by LoginInterceptor
        guard !LoginManager.sharedInstance.isUserLoggedIn else {
            return
        }

        // Handled by a ProductViewControllerFactory
        let productViewController = ProductViewController(nibName: "ProductViewController", bundle: nil)

        // Handled by ProductViewControllerContextTask
        productViewController.productID = productID

        // Handled by NavigationControllerStep and UINavigationController.push
        let navigationController = UINavigationController(rootViewController: productViewController)

        // handled by DefaultActions.PresentModally
        present(navigationController, animated: true) { [weak self]
            // Handled by ProductViewControllerPostTask
            self?.analyticsManager.trackProductView(productID: productID)
        }
    }

}

In the example without RouteComposer the code may seem simpler, however, everything is hardcoded in the actual function implementation. RouteComposer allows you to split everything into small reusable pieces and store navigation configuration separately from your view logic. Also, the above implementation will grow dramatically when you try to add Universal Link support to your app. Especially if you will have to choose from opening ProductViewController from a universal link if it is already present on the screen or not and so on. With the library, each of your view controllers is deep linkable by nature.

As you can see from the examples above the Router does not do anything that tweaks UIKit basis. It just allows you to break the navigation process into small reusable pieces. The router will call them in a proper order based on the configuration provided. The library does not break the rules of VIPER or MVVM architectural patterns and can be used in parallel with them.

See example app for other examples of defining routing configurations and instantiating router.

Deep-linking

With RouteComposer every view controller becomes deep-linkable out of the box. You can also provide different configuration in case the screen is being opened using universal link. See Example app for more information.

    let router = DefaultRouter()

    func application(_ application: UIApplication,
                     open url: URL,
                     sourceApplication: String?,
                     annotation: Any) -> Bool {
        guard let productID = extractProductId(from: url) else {
            return false
        }
        try? router.navigate(to: Configuration.productScreen, with: productID)
        return true
    }

Troubleshooting

If for some reason you are unsatisfied with the result and you think that it is the Routers issue, or you found that your particular case is not covered, you can always temporarily replace the router with your custom implementation and implement simple routing yourself. Please, create a new issue and we will try to fix the issue as soon as possible.

Example:

     func goToProduct(with productId: UUID) {
        // If view controller with this product id is present on the screen - do nothing
        guard ProductViewControllerFinder(options: .currentVisibleOnly).getViewController(with: productId) == nil else {
            return
        }
        
        /// Otherwise, find visible `UINavigationController`, build `ProductViewController`
        guard let navigationController = ClassFinder<UINavigationController, Any?>(options: .currentVisibleOnly).getViewController(),
              let productController = try? ProductViewControllerFactory().execute(with: productId) else {
            return
        }
        
        /// Apply context task if necessary
        try? ProductViewControllerContextTask().execute(on: productController, with: productId)

        /// Push `ProductViewController` into `UINavigationController`
        navigationController.pushViewController(productController, animated: true)
    }

SwiftUI:

RouteComposer is compatible with SwiftUI. See example app for the details.

Advanced Configuration:

You can find more configuration examples here.

Contributing

RouteComposer is in active development, and we welcome your contributions.

If you’d like to contribute to this repo, please read the contribution guidelines.

License

RouteComposer is distributed under the MIT license.

RouteComposer is provided for your use, free-of-charge, on an as-is basis. We make no guarantees, promises or apologies. Caveat developer.

Articles

English:

• Composition of UIViewControllers and navigation between them
• Going deeper into the RouteComposer configuration
• Coordinator Pattern’s Issues & What is RouteComposer

Russian:

• Композиция UIViewController-ов и навигация между ними
• Примеры конфигурации UIViewController-ов используя RouteComposer
• Проблемы паттерна Координатор и при чем тут RouteComposer

Author

Evgeny Kazaev, [email protected]. Twitter ekazaev

I am happy to answer any questions you may have. Just create a new issue.