406 words (approximately 2 mins)

overview

router component

(In this section, Navigation is an injected NavigationManager)
The Router component enables routing:

App.razor

<Router AppAssembly="@typeof(Program).Assembly">
    <Found Context="routeData">
        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
    </Found>
    <NotFound>
        <p>Sorry, there's nothing at this address.</p>
    </NotFound>
</Router>

focus

Set the UI focus to an element based on a CSS selector. When the Router navigates to a new page, this sets the focus to the page’s top-level header:

<FocusOnNavigate RouteData="@routeData" Selector="h1" />

provide custom content when content not found

Use the NotFound template:
App.razor

<Router AppAssembly="@typeof(Program).Assembly">
    <Found Context="routeData">
        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
    </Found>
    <NotFound>
        <p>Sorry, there's nothing at this address.</p>
    </NotFound>
</Router>

tell router to search additional assemblies for components

Use the AdditionalAssemblies parameter:

<Router
    AppAssembly="@typeof(App).Assembly"
    AdditionalAssemblies="new[] { typeof(Component1).Assembly }">
    @* ... Router component elements ... *@
</Router>

routing urls with dots

For hosted Blazor WASM and Blazor Server apps

  • The default route template assumes that, if the last segment of a request URL contains a dot, a file is requested.
  • Example: if the request URL is /example/some.thing the Router interprets this to be a request for the file some.thing.

If some.thing is a route parameter value, the app must be configured with a custom route template.

  • For Blazor WASM’s Server project, in Program.cs:
    app.MapFallbackToFile("/example/{param?}", "index.html");
  • For Blazor Server, in Program.cs:
    app.MapFallbackToPage("/example/{param?}", "/_Host");

handling asynchronous navigation events

Router has an OnNavigateAsync handler. It is passed a NavigationContext. It is invoked when:

  1. A user visits a route for the first time by navigating to it directly in their browser
  2. A user navigates to a new route using a link or the NavigationManager.NavigateTo invocation

App.razor

<Router AppAssembly="@typeof(App).Assembly" 
    OnNavigateAsync="@OnNavigateAsync">
    ...
</Router>

@code {
    private async Task OnNavigateAsync(NavigationContext context)
    {
        // ...
    }
}

Note: In Blazor Server and hosted Blazor WASM apps, when prerendering, OnNavigateAsync is executed twice: one when the endpoint component is initially rendered (statically), and again when the browser renders the endpoint component.

  • App.razor can store the NavigationContext for use in OnAfterRender{Async}, which has a bool firstRender that can be checked.

handling cancellations

The NavigationContext passed to OnNavigateAsync contains a CancellationToken property. This CancellationToken is set whenever a new navigation event occurs. When implementing OnNavigateAsync, the callback must throw if cancellation is requested to avoid unintended behavior.

<Navigating> Content

The Router can indicate to the user that a page transition is occurring: App.razor

@using Microsoft.AspNetCore.Components.Routing

<Router>
    <!-- ... -->
    <Navigating>
        <p>Loading the requested page&hellip;</p>
    </Navigating>
    <!-- ... -->
</Router>

NavLink and NavMenu Components

See notes in Components.