MonarchRouter 1.1.2

MonarchRouter 1.1.2

Maintained by Eliah Snakin, Eliah Snakin.

  • By
  • nikans


Version License Platform

Monarch Router

A lightweight yet powerful functional state-based router written in Swift.

Common URL conventions are used for routing. It's designed for you to feel at home if you ever developed a server-side app routing.

Monarch Router is a declarative routing handler that decouples ViewControllers from each other via Coordinator and Presenters. It fits right in with Redux style state flow and reactive frameworks.

The Coordinator is constructed by declaring a route hierarchy mapped with a URL structure. Presenters abstract UI creation and modification.

Monarch Router is distributed via SPM and Cocoapods.

Monarch butterflies weight less than 1 gram but cover thousands of miles during their migration. It's considered an iconic pollinator and one of the most beautiful butterfly species.


  • Navigating complex ViewControlles hierarchy and unwinding on path change.
  • Parsing and passing route parameters to endpoints, following URL conventions.
  • Deeplinking to handle Push Notifications, Shortcuts and Universal Links.
  • Navigating forks (tabbar-like presenters).
  • Navigating stacks (i.e. navigation controller).
  • Opening and dismissing modals, with their own hierarchy.
  • Switching top-level app sections via changing the window's rootViewController.
  • Scenes handling.
  • Handling navigation in universal apps. (PRs welcome!)
  • Properly abstracting Router layer to handle navigation in macOS apps.


  • Router: your app's routing Coordinator (root RoutingNode with children); or more broadly speaking, this whole thing.

  • RoutingNode: a structure that collects functions together that are related to the same endpoint or intermidiate routing point with children. Each RoutingNode also requires a Presenter, to which any required changes are passed.

  • RoutePresenter: a structure used to create and configure a Presentable (i.e. UIViewController). There're several types of presenters: endpoint, stack (for navigation tree), fork (for tabs), switcher (for uncoupled apps sections).

  • Presentable: an actual object to be displayed (i.e. UIViewController).

  • Lazy Presenter: a lazy wrapper around a presenter creation function that wraps presenter scope, but the Presentable does not get created until invoked.

  • RoutingRequest: a URL or URL-like structure used to define the endpoint you want to navigate to.

  • Route: a structure that defines matching rules for a RoutingRequest to trigger routing to a certain RoutingNode.

  • RouterStore: holds the State for the router. Provides a method to dispatch a RoutingRequest and modify the State via a Reducer.

  • RouterState: holds the stack of active RoutingNodes.

  • RouterReducer: a function to calculate a new State. Implements navigation via RoutingNode's callback. Unwinds unused RoutingNodes.

Basic flow

  1. RouteRequest is dispatched on a RouterStore. The request is a URL, or URL-like structure.
  2. The new State is calculated by a reducer, matching the request against a Coordinator hierarchy. Each Node in the hierarchy is associated with a Route (a matching rule) and a Presenter, that abstracts the UI.
  3. Unused nodes and corresponding presentables are being unwound, new presentables hierarchy remade based on caclulated State.


The example project illustrates the basic usage of the router, as well as some not-trivial use cases, such as modals handling and deeplinking.

If you prefer using Cocoapods, rather than SPM, clone the repo, and run pod install from the Example directory first.

See Example App.

How to use

0. Start with creating a RouterStore.

Persist it in your App- or SceneDelegate.

// Initializing Router and setting root VC
let coordinator = appCoordinator()
let router = RouterStore(router: coordinator)

self.appRouter = router

1. Define your App's Routes.

Routes are rules used to match against RoutingRequests.

/// Your app custom Routes
enum AppRoute: String, RouteType
    case login = "login"
    case today = "today"
    case story = "today/story/:type/:id"
    case books = "books"
    case book  = "books/:id"

A route is consisted of RouteComponents. These components are matched to the RouteRequest's PathComponents (see below).

There are several ways to define a Route:

String conforms to RouteType.

  • Components are separated with /
  • Constant components are just strings (i.e. login)
  • Parameter components are prefixed with :
  • To match anything for a component use :_
  • To match everything to the end of the path use ...

Use built-in RouteString structure to create RegExp-validated routes.

typealias ParameterValidation = (name: String, pattern: String)
init(_ predicate: String, parametersValidation: [ParameterValidation]? = nil)
  • Use the stated above rules to set a predicate string.
  • Optionally add a ParameterValidation array, where name is a parameter name (without :) and pattern is a RegExp.

Array of RouteComponents conforms to RouteType.

Build your Route with RouteComponent enum:

enum RouteComponent 
    /// Matches a constant component
    case constant(String)
    /// Matches a parameter component
    /// - parameter name: parameter name to match
    /// - parameter isMatching: optional closure to match parameter value
    case parameter(name: String, isMatching: ((_ value: Any) -> Bool)? )
    /// Matches any path component for a route component
    case anything
    /// Matches any path to the end
    case everything

1.1. Optionally define a set of RoutingRequests.

RoutingRequest is matched against Routes associated with a RoutingNode.

To make things easy, Monarch Router uses URLs or valid URL-like Strings to trigger routing.

URL parts available:

  • path components (books/:id)
  • query items (?name=eliah)
  • fragment (#documentation)

You can dispatch URL or String directly. Alternatively you can create a custom enum:

enum AppRoutingRequest: RoutingRequestType
    case login
    case today
    case story(type: String, id: Int, title: String)
    case books
    case book(id: Int, title: String?)

    var request: String {
        switch self {
        case .login:
        return "login"

        case .today:
        return "today"

        case .story(let type, let id, let title):
        return "today/story/\(type)/\(id)?title=\(title)"

        case .books:
        return "books"

        case .book(let id, let title):
        return "books/\(id)?title=\(title ?? "")"

If for your convenience you've decided to define a custom RoutingRequestType enum, you'll need a resolver function. Since here we're mapping our requests to a String, we'll use it's built-in resolver.

func resolve(for route: RouteType) -> RoutingResolvedRequestType {
    return request.resolve(for: route)

Matched Presenters can be parametrized with resolved RouteParameters object (see below).

Only path parameters are used for matching, though you can configure your presentable based on query parameters and fragment.

1.2. Dispatch routing requests on the RouterStore object


You may want to hide your RouterStore implementation behind a specialized ProvidesRouteDispatch protocol, i.e:

protocol ProvidesRouteDispatch: class
    /// Extension method to change the Route.
    /// - parameter request: `AppRoutingRequest` to navigate to.
    func dispatch(_ request: AppRoutingRequest)

extension RouterStore: ProvidesRouteDispatch { 
    func dispatch(_ request: AppRoutingRequest) {

But first we need to create a Coordinator.

2. Create your app's Coordinator

The Coordinator is a hierarchial RoutingNode structure.

/// Creating the app's Coordinator hierarchy.
func appCoordinator() -> RoutingNodeType
    // Top level app sections' switcher

        // Login 
        // (section 0)
        RoutingNode(lazyPresenter(for: .login))

        // Tabbar 
        // (section 1)

                // Today nav stack
                // (tab 0)

                    // Today
                    RoutingNode(lazyPresenter(for: .today))
                        .endpoint(, modals: [

                        // Story 
                        // (presented modally)
                        RoutingNode(lazyPresenter(for: .story))

                // Books nav stack
                // (tab 1)

                    // Books
                    // (master)
                    RoutingNode(lazyPresenter(for: .books))
                        .endpoint(AppRoute.books, children: [

                        // Book
                        // (detail)
                        RoutingNode(lazyPresenter(for: .book))

Depending on it's Presenter, a RoutingNode can execute one of four types of behavior:

  • endpoint
  • stack (i.e. navigation tree)
  • fork (i.e. tabs)
  • switcher (decoupled app's sections)

Each RoutingNode either matches a RoutingRequest against it's Route (i.e. .endpoint( or against its childrens' routes (not-endpoint type nodes). The suitable sub-hierarchy is then selected, the RouterState is reduced to a new one.

The new nodes stack's Presenters are then instantiating their Presentables (i.e. UIViewControllers) if necessary, and the app's navigation hierarchy is rebuilt automatically.

UI magic is abstracted in the Presenters.

3. Create Presenters

Presentable configuration

The main goal of presenters is to create a Presentable object. So, when you define a Presenter you have to pass a closure for the creation of a Presentable: getPresentable: () -> (UIViewController). Currently, only UIViewController subtypes are supported.

If a Presenter was called with some RouteParameters, an optional closure allowing for the Presentable configuration is called: setParameters: ((_ parameters: RouteParameters, _ presentable: UIViewController) -> ()).

Note: Conform your Presentable to RouteParametrizedPresentable to handle this automatically.

An optional closure unwind: (_ presentable: UIViewController) -> () is called when the node is no longer selected. You can set it if your Presentable requires any special behavior.

Important: Every Presenter can be instantiated directly or lazily. It's advised to use lazy initialization in your Coordinator hierarchy, otherwise all the presentables will be instantiated on the app launch.

Built-in Presenters


is used for endpoint presentation.

The endpoint Presenter is able to present and dismiss modals with the hierarchy of their own. The corresponding closures are called:

/// Callback executed when a modal view is requested to be presented.
presentModal: (_ modal: UIViewController, _ over: UIViewController) -> ()

/// Callback executed when a presenter is required to close its modal.
dismissModal: ((_ modal: UIViewController)->())

Modal presentation works out of the box, so you may want to use those for the special behavior only.


is used for tabbar-style presentation.

Special closures are used to configurate a Presentable (i.e. UITabBarController)

/// Sets the options for Router to choose from
setOptions: (_ options: [UIViewController], _ container: UIViewController) -> ()

/// Sets the specified option as currently selected.
setOptionSelected: (_ option: UIViewController, _ container: UIViewController) -> ()

Use .junctionsOnly dispatch option when switching to a tab by it's root Route, when the tab already contains presented stack.


is used to organize other Presenters in a navigation stack (i.e. UINavigationController).

/// Sets the navigation stack
setStack: (_ stack: [UIViewController], _ container: UIViewController) -> ()

/// Presets root Presentable when the stack's own Presentable is requested
prepareRootPresentable: (_ rootPresentable: UIViewController, _ container: UIViewController) -> ()

is used to switch between decoupled app sections (i.e. login sequence, main sequence...)

/// Sets the specified option as currently selected.
setOptionSelected: (_ option: UIViewController) -> ()

This Presenter may probably don't have a Presentable.

Example Presenters

The Example app contains several useful Presenters, not made part of the library, i.e:

  • UITabBarController presenter built on RoutePresenterFork with a delegate to dispatch routing request on tap.
  • UINavigationController presenter built on RoutePresenterStack with relevant pop/push/etc behavior.
  • Sections switch presenter built on RoutePresenterSwitcher, with ability to set window's rootViewController.

Principle concepts

UI is a representation of State

As the State changes over time, so will the UI projection of that State. Given any State value the UI must be predictable and repeatable.

Device dependent state should be separate from the router State.

Displaying the same State on a phone and tablet for example, can result in different UIs. The device dependent state should remain on that device. An OS X and iOS app can use the same State and logic classes and interchange Routers for representing the State.

Not fully implemented yet. PRs welcome!

UI can generate actions to update the nodes stack in the State

The user tapping a back button is easy to capture and generate an action that updates the State, which causes the UI change. But a user 'swiping' back a view is harder to capture. It should instead generate an action on completion to update the State. Then, if the current UI already matches the new State no UI changes are necessary.


Swift Package Manager

Using Xcode UI: go to your Project Settings -> Swift Packages and add [email protected]:nikans/MonarchRouter.git there.

To integrate using Apple's Swift package manager, without Xcode integration, add the following as a dependency to your Package.swift:

.package(url: "[email protected]:nikans/MonarchRouter.git", .upToNextMajor(from: "1.1.0"))


To install it, simply add the following line to your Podfile:

pod 'MonarchRouter', '~> 1.1'

You may find the last release version here.


Currently only iOS/iPhone 8.0+ is properly supported, but theoretically it's easyly extended to support Universal apps. MacOS support requires a new layer of abstraction with generics and stuff, and I think that it's clearer to use as it is for now. But you are very welcome to contribute!

  • iOS/iPhone
  • iOS/Universal
  • macOS


Eliah Snakin: [email protected]

Monarch Router emerged from crysalis of Featherweight Router.


MonarchRouter is available under the MIT license. See the LICENSE file for more info.