Ariadne's thread, named for the legend of Ariadne, is the solving of a problem with multiple apparent means of proceeding - such as a physical maze, a logic puzzle, or an ethical dilemma - through an exhaustive application of logic to all available routes.

Wikipedia

Ariadne is an extensible routing framework, built with composition and dependency injection principles in mind. It helps to create transitions and routes, that abstract away view controller building and presentation logic to make it reusable and compact.

UIKit has a routing problem. All view controller presentation and dismissal methods happen in view controller, which a lot of times leads to bloated view controller, because all view controller building, dependency injection and transitions that also happen there.

This leads to massive view controllers, that cannot be easily tested, and code, that is hard to reuse across different view controller instances. One solution to those problems is to separate view controller building, and transition code in separate object, commonly called Router. And even though only some architectures like VIPER promote Router as required component, I would argue that app with any other architecture can be drastically improved by having at least some form of routing.

This is where Ariadne comes in. It is a framework, that provides view controller building mechanisms, transition and routing classes to abstract all this logic from view controller in architecture-agnostic way.

Let's say, for example, that you need to present user profile inside UINavigationController. Usually, in MVC app without any libraries, you would do something like this:

let storyboard = UIStoryboard(named: "User", bundle: nil)
let userController = storyboard.instantiateViewController(withIdentifier: "UserViewController")
userController.user = user
let navigation = UINavigationController(rootViewController: userController)
present(navigation, animated: true)

With Ariadne, this code is no longer tied to current view controller and can look like this:

let route = Storyboards.User.userViewController.builder.embeddedInNavigation().presentRoute()
router.navigate(to: route, with: user)

Note: this specific example requires SwiftGen integration, described in SwiftGen integration guide. Without SwiftGen Storyboards.User.userViewController.builder could be replaced by any custom view controller builder.

• iOS 10+
• macOS 10.12+
• tvOS 10+
• watchOS 3+
• Xcode 10 / Swift 4.2 and higher

• Add package into Project settings -> Swift Packages

pod 'Ariadne'

Ariadne architecture fundamentally starts with ViewBuilder. Because view controllers are so tightly coupled with their views on iOS, UIViewController is considered to be a view and is typealiased to ViewController.

Note: on watchOS ViewController is a typealias for WKInterfaceController, and on macOS for NSViewController for similar reasons.

Definition of ViewBuilder is simple - it builds a ViewController out of provided Context:

protocol ViewBuilder {
    associatedtype ViewType: ViewController
    associatedtype Context
    func build(with context: Context) throws -> ViewType
}

Out of the box, Ariadne provides builders for:

• UINavigationController
• UITabBarController
• UISplitViewController

Second building block of the framework are ViewTransition objects, that are needed to perform transition between views. Out of the box, following transitions are supported:

• UINavigationController transitions - push, pop, pop to root, pop to view controller, replace controllers in navigation stack
• UIViewController presentations - present, dismiss
• UIWindow root view controller transition to perform switch of the root view controller with animation.

ViewBuilder and ViewTransition object can be combined together to form a performable Route. For example, given AlertBuilder, here's how creating a route for an alert might look like with Ariadne:

let alertRoute = AlertBuilder().presentRoute()

Notice how presentRoute method is called identically for AlertBuilder and any UIViewController builders. By leveraging protocol extensions on ViewBuilder any transitions and routes can be reused on ViewBuilder instance. To see examples of how ViewBuilder protocol can be implemented and extended, please refer to Implementing view builders guide.

Last, but not least, Router object ties everything together and allows you to actually perform routes:

router.navigate(to: alertRoute, with: alertModel, completion: { _ in
    // Route has completed
})

Router uses RootViewProvider to find which view controller is a root one in a view hierarchy. On iOS and tvOS RootViewProvider is an interface for UIWindow and allows Router to get root view controller of view hierarchy. But on other platforms as well as application extensions UIApplication shared window is not accessible, and in that cases RootViewProvider may be different, for example in iMessage apps MSMessagesAppViewController may play similar role.

ViewFinder object traverses view hierarchy starting from root view to find view controller that is currently visible on screen. On iOS and tvOS Ariadne provides implementation of CurrentlyVisibleViewFinder class, that recursively searches UIViewController, UINavigationController and UITabBarController to find which view controller is currently visible, but on other platforms and in other scenarios you might want to roll with your implementation or subclass of CurrentlyVisibleViewFinder, if your view hierarchy contains other view controller containers.

SwiftGen is a powerful code generator, that can be used to set you free from using String-based API, that is cumbersome and error-prone. For example with storyboards, SwiftGen is able to generate code required for instantiating view controllers and makes this code to guarantee on compile-time that storyboard and view controller exist. Ariadne can build on top of that, producing a neat syntax for route building, like so:

let route = Storyboards.User.userViewController.builder.embeddedInNavigation().presentRoute()

To find out, how this can be achieved, refer to SwiftGen integration guide.

Different applications can have completely different architectures and requirements. To see examples of simple dependency injection see SwiftGen integration and for more advanced dependency injection with dependency containers like Dip, head to Advanced dependency injection examples guide.

To find out more about project future goals and vision, please read the Vision document.

You can find complete project documentation here.

iOS Example project can be found in Ariadne.xcodeproj and contains:

• Root view controller animated change
• Push/pop, present/dismiss
• Peek & Pop
• Custom transition and presentation
• Update currently visible view.

Ariadne is released under a MIT license. See LICENSE for more information.