ASP.NET Core Blazor routing

By Luke Latham

Learn how to route requests and how to use the NavLink component to create navigation links in Blazor apps.

ASP.NET Core endpoint routing integration

Blazor Server is integrated into ASP.NET Core Endpoint Routing. An ASP.NET Core app is configured to accept incoming connections for interactive components with MapBlazorHub in Startup.Configure:

app.UseRouting();

app.UseEndpoints(endpoints =>
{
    endpoints.MapBlazorHub();
    endpoints.MapFallbackToPage("/_Host");
});

Route templates

The Router component enables routing to each component with a specified route. The Router component appears in the App.razor file:

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

When a .razor file with an @page directive is compiled, the generated class is provided a RouteAttribute specifying the route template.

At runtime, the RouteView component:

  • Receives the RouteData from the Router along with any desired parameters.
  • Renders the specified component with its layout (or an optional default layout) using the specified parameters.

You can optionally specify a DefaultLayout parameter with a layout class to use for components that don't specify a layout. The default Blazor templates specify the MainLayout component. MainLayout.razor is in the template project's Shared folder. For more information on layouts, see ASP.NET Core Blazor layouts.

Multiple route templates can be applied to a component. The following component responds to requests for /BlazorRoute and /DifferentBlazorRoute:

@page "/BlazorRoute"
@page "/DifferentBlazorRoute"

<h1>Blazor routing</h1>

Important

For URLs to resolve correctly, the app must include a <base> tag in its wwwroot/index.html file (Blazor WebAssembly) or Pages/_Host.cshtml file (Blazor Server) with the app base path specified in the href attribute (<base href="/">). For more information, see Host and deploy ASP.NET Core Blazor.

Provide custom content when content isn't found

The Router component allows the app to specify custom content if content isn't found for the requested route.

In the App.razor file, set custom content in the NotFound template parameter of the Router component:

<Router AppAssembly="typeof(Startup).Assembly">
    <Found Context="routeData">
        <RouteView RouteData="@routeData" DefaultLayout="@typeof(MainLayout)" />
    </Found>
    <NotFound>
        <h1>Sorry</h1>
        <p>Sorry, there's nothing at this address.</p> b
    </NotFound>
</Router>

The content of <NotFound> tags can include arbitrary items, such as other interactive components. To apply a default layout to NotFound content, see ASP.NET Core Blazor layouts.

Route to components from multiple assemblies

Use the AdditionalAssemblies parameter to specify additional assemblies for the Router component to consider when searching for routable components. Specified assemblies are considered in addition to the AppAssembly-specified assembly. In the following example, Component1 is a routable component defined in a referenced class library. The following AdditionalAssemblies example results in routing support for Component1:

<Router AppAssembly="typeof(Program).Assembly" AdditionalAssemblies="new[] { typeof(Component1).Assembly }> ...

Route parameters

The router uses route parameters to populate the corresponding component parameters with the same name (case insensitive):

@page "/RouteParameter"
@page "/RouteParameter/{text}"

<h1>Blazor is @Text!</h1>

@code {
    [Parameter]
    public string Text { get; set; }

    protected override void OnInitialized()
    {
        Text = Text ?? "fantastic";
    }
}

Optional parameters aren't supported for Blazor apps in ASP.NET Core 3.0 Preview. Two @page directives are applied in the previous example. The first permits navigation to the component without a parameter. The second @page directive takes the {text} route parameter and assigns the value to the Text property.

Route constraints

A route constraint enforces type matching on a route segment to a component.

In the following example, the route to the Users component only matches if:

  • An Id route segment is present on the request URL.
  • The Id segment is an integer (int).
@page "/Users/{Id:int}"

<h1>The user Id is @Id!</h1>

@code {
    [Parameter]
    public int Id { get; set; }
}

The route constraints shown in the following table are available. For the route constraints that match with the invariant culture, see the warning below the table for more information.

Constraint Example Example Matches Invariant
culture
matching
bool {active:bool} true, FALSE No
datetime {dob:datetime} 2016-12-31, 2016-12-31 7:32pm Yes
decimal {price:decimal} 49.99, -1,000.01 Yes
double {weight:double} 1.234, -1,001.01e8 Yes
float {weight:float} 1.234, -1,001.01e8 Yes
guid {id:guid} CD2C1638-1638-72D5-1638-DEADBEEF1638, {CD2C1638-1638-72D5-1638-DEADBEEF1638} No
int {id:int} 123456789, -123456789 Yes
long {ticks:long} 123456789, -123456789 Yes

Warning

Route constraints that verify the URL and are converted to a CLR type (such as int or DateTime) always use the invariant culture. These constraints assume that the URL is non-localizable.

Routing with URLs that contain dots

In Blazor Server apps, the default route in _Host.cshtml is / (@page "/"). A request URL that contains a dot (.) isn't matched by the default route because the URL appears to request a file. A Blazor app returns a 404 - Not Found response for a static file that doesn't exist. To use routes that contain a dot, configure _Host.cshtml with the following route template:

@page "/{**path}"

The "/{**path}" template includes:

  • Double-asterisk catch-all syntax (**) to capture the path across multiple folder boundaries without encoding forward slashes (/).
  • A path route parameter name.

For more information, see Routing in ASP.NET Core.

Use a NavLink component in place of HTML hyperlink elements (<a>) when creating navigation links. A NavLink component behaves like an <a> element, except it toggles an active CSS class based on whether its href matches the current URL. The active class helps a user understand which page is the active page among the navigation links displayed.

The following NavMenu component creates a Bootstrap navigation bar that demonstrates how to use NavLink components:

<div class="@NavMenuCssClass" @onclick="@ToggleNavMenu">
    <ul class="nav flex-column">
        <li class="nav-item px-3">
            <NavLink class="nav-link" href="" Match="NavLinkMatch.All">
                <span class="oi oi-home" aria-hidden="true"></span> Home
            </NavLink>
        </li>
        <li class="nav-item px-3">
            <NavLink class="nav-link" href="MyComponent" Match="NavLinkMatch.Prefix">
                <span class="oi oi-plus" aria-hidden="true"></span> My Component
            </NavLink>
        </li>
    </ul>
</div>

There are two NavLinkMatch options that you can assign to the Match attribute of the <NavLink> element:

  • NavLinkMatch.All – The NavLink is active when it matches the entire current URL.
  • NavLinkMatch.Prefix (default) – The NavLink is active when it matches any prefix of the current URL.

In the preceding example, the Home NavLink href="" matches the home URL and only receives the active CSS class at the app's default base path URL (for example, https://localhost:5001/). The second NavLink receives the active class when the user visits any URL with a MyComponent prefix (for example, https://localhost:5001/MyComponent and https://localhost:5001/MyComponent/AnotherSegment).

Additional NavLink component attributes are passed through to the rendered anchor tag. In the following example, the NavLink component includes the target attribute:

<NavLink href="my-page" target="_blank">My page</NavLink>

The following HTML markup is rendered:

<a href="my-page" target="_blank" rel="noopener noreferrer">My page</a>

URI and navigation state helpers

Use Microsoft.AspNetCore.Components.NavigationManager to work with URIs and navigation in C# code. NavigationManager provides the event and methods shown in the following table.

Member Description
Uri Gets the current absolute URI.
BaseUri Gets the base URI (with a trailing slash) that can be prepended to relative URI paths to produce an absolute URI. Typically, BaseUri corresponds to the href attribute on the document's <base> element in wwwroot/index.html (Blazor WebAssembly) or Pages/_Host.cshtml (Blazor Server).
NavigateTo Navigates to the specified URI. If forceLoad is true:
  • Client-side routing is bypassed.
  • The browser is forced to load the new page from the server, whether or not the URI is normally handled by the client-side router.
LocationChanged An event that fires when the navigation location has changed.
ToAbsoluteUri Converts a relative URI into an absolute URI.
ToBaseRelativePath Given a base URI (for example, a URI previously returned by GetBaseUri), converts an absolute URI into a URI relative to the base URI prefix.

The following component navigates to the app's Counter component when the button is selected:

@page "/navigate"
@inject NavigationManager NavigationManager

<h1>Navigate in Code Example</h1>

<button class="btn btn-primary" @onclick="NavigateToCounterComponent">
    Navigate to the Counter component
</button>

@code {
    private void NavigateToCounterComponent()
    {
        NavigationManager.NavigateTo("counter");
    }
}