router.md

Router

The router is the root of all navigation and presentation. It is in charge of communicating with the NavigationState and the PresentationState to show view models. Most notably, the router does things like determine which hints to give the PresentationState and manipulates the NavigationState to be in the correct state for view models.

interface IRouter
{
    Task ShowAsync(Type viewModel, object vmParams);
}

The interface for IRouter is kept to the absolute minimum to help with testing. Additionally, a couple of extension methods can be added to help consumablility.

static class RouterExtensions
{
    public static Task ShowAsync<TViewModel>(this IRouter router, object vmParams) => 
        router.ShowAsync(typeof(TViewModel), vmParams);
    public static Task ShowAsync<TViewModel>(this IRouter router) => 
        router.ShowAsync<TViewModel>(null);
}

The actions that a router takes are meant to be composed with a builder. A basic router builder might look like this:

interface IRouterBuilder
{
    IRouterBuilder When(Type vmType, Func<IRouteBuilder, IRouteBuilder> buildRoute);
    IRouter Build();
}

interface IRouteBuilder
{
    // Instructs the router to tell the PresentationState to use the given
    // view/presenter type when the route is hit.
    IRouteBuilder Present(Type viewType);

    // Instructs the router to manipulate the NavigationState
    // when the route is hit.
    IRouteBuilder NavigateBack(Func<object, bool> goBackWhile);
    IRouteBuilder Navigate();
}

Along with relevent extension methods:

static class RouterBuilderExtensions
{
    public static IRouterBuilder When<TViewModel>(this IRouterBuilder builder, Func<IRouteBuilder, IRouteBuilder> buildRoute) =>
            builder.When(typeof(TViewModel), buildRoute);
    public static IRouteBuilder When<TViewModel>(this IRouterBuilder builder) => 
            builder.When<TViewModel>(null);
}

static class RouteBuilderExtensions
{
    public static IRouteBuilder Present<TView>(this IRouteBuilder route) =>
            route.Present(typeof(TView)); 
    public static IRouteBuilder NavigateFrom<TParentViewModel>(this IRouteBuilder route) =>
            route.NavigateBack(vm => !(vm is TParentViewModel));
}