Elmish-navigation ease the navigation for application that follows MVU pattern. It makes the creation and management of pages and models less tedious.

The library allow to create each page as if it were an independant application with their own init, update and view workflow.

The library is fully written in F# and use dotnet SDK. It can be installed through dotnet nuget:

dotnet add package Elmish.Navigation

or paket:

paket add Elmish.Navigation

Elmish-navigation is a plugin that extends Program type from Elmish. Like others Program plugin, you must call it once the program is created. The name of the method is withNavigation.

Here is the minimum setup to use it:

module App

open Elmish
open Elmish.Navigation

type Model = {
    Counter: int }

let init () = 
    { Counter = 0 }, []

let update msg model =
    model, []

module R = Fable.ReactNative.Helpers
 
let view model dispatch navigation =
    R.view [][]

Program.mkProgram init update view
|> Program.withNavigation [] "Home"
|> Program.withConsoleTrace
|> Program.run

Program.withNavigation takes two arguments:

• Pages: It's a list of name associated to a page template.
• Default: Name of the default page used at the first screen.

Few notes regarding the way the library handle messages and pages. We make a clear distinction between message sent by the App and message sent from a page.

We called App the init/update/view that you have at the root level of your application, the ones passed to the mkProgram method when you init the app. You will probably use the app methods to handle messags and views that are global to your application.

And we called Page the individuals init/update/view of each pages. Messages, models and views from Page are usually constrained to the page and does not leak outside.

To resume, when sending messages from the update or dispatch of the App, they will be received by the update method of the App. And when sending from a Page, it will be received by the update method of the same page.