Add NotFoundPage to Router

src/Components/Components/src/PublicAPI.Unshipped.txt

@@ -1,6 +1,8 @@
 #nullable enable
 Microsoft.AspNetCore.Components.NavigationManager.NotFoundEvent -> System.EventHandler<System.EventArgs!>!
 virtual Microsoft.AspNetCore.Components.NavigationManager.NotFound() -> void
+Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.get -> System.Type!
+Microsoft.AspNetCore.Components.Routing.Router.NotFoundPage.set -> void
 Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager.ComponentStatePersistenceManager(Microsoft.Extensions.Logging.ILogger<Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager!>! logger, System.IServiceProvider! serviceProvider) -> void
 Microsoft.AspNetCore.Components.Infrastructure.ComponentStatePersistenceManager.SetPlatformRenderMode(Microsoft.AspNetCore.Components.IComponentRenderMode! renderMode) -> void
 Microsoft.AspNetCore.Components.Infrastructure.RegisterPersistentComponentStateServiceCollectionExtensions

src/Components/Components/src/Routing/Router.cs

@@ -3,11 +3,13 @@
 
 #nullable disable warnings
 
+using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Reflection.Metadata;
 using System.Runtime.ExceptionServices;
 using Microsoft.AspNetCore.Components.HotReload;
 using Microsoft.AspNetCore.Components.Rendering;
+using Microsoft.AspNetCore.Internal;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.DependencyInjection;
 
@@ -70,6 +72,13 @@ static readonly IReadOnlyDictionary<string, object> _emptyParametersDictionary
     [Parameter]
     public RenderFragment NotFound { get; set; }
 
+    /// <summary>
+    /// Gets or sets the page content to display when no match is found for the requested route.
+    /// </summary>
+    [Parameter]
+    [DynamicallyAccessedMembers(LinkerFlags.Component)]
+    public Type NotFoundPage { get; set; } = default!;
+
     /// <summary>
     /// Gets or sets the content to display when a match is found for the requested route.
     /// </summary>
@@ -132,6 +141,22 @@ public async Task SetParametersAsync(ParameterView parameters)
             throw new InvalidOperationException($"The {nameof(Router)} component requires a value for the parameter {nameof(Found)}.");
         }
 
+        if (NotFoundPage != null)
+        {
+            if (!typeof(IComponent).IsAssignableFrom(NotFoundPage))
+            {
+                throw new InvalidOperationException($"The type {NotFoundPage.FullName} " +
+                    $"does not implement {typeof(IComponent).FullName}.");
+            }
+
+            var routeAttributes = NotFoundPage.GetCustomAttributes(typeof(RouteAttribute), inherit: true);
+            if (routeAttributes.Length == 0)
+            {
+                throw new InvalidOperationException($"The type {NotFoundPage.FullName} " +
+                    $"does not have a {typeof(RouteAttribute).FullName} applied to it.");
+            }
+        }
+
         if (!_onNavigateCalled)
         {
             _onNavigateCalled = true;
@@ -251,7 +276,22 @@ internal virtual void Refresh(bool isNavigationIntercepted)
                 // We did not find a Component that matches the route.
                 // Only show the NotFound content if the application developer programatically got us here i.e we did not
                 // intercept the navigation. In all other cases, force a browser navigation since this could be non-Blazor content.
-                _renderHandle.Render(NotFound ?? DefaultNotFoundContent);
+                _renderHandle.Render(builder =>
+                {
+                    if (NotFoundPage != null)
+                    {
+                        builder.OpenComponent(0, NotFoundPage);
+                        builder.CloseComponent();
+                    }
+                    else if (NotFound != null)
+                    {
+                        NotFound(builder);
+                    }
+                    else
+                    {
+                        DefaultNotFoundContent(builder);
+                    }
+                });
             }
             else
             {

src/Components/test/E2ETest/Tests/GlobalInteractivityTest.cs

@@ -22,12 +22,16 @@ public class GlobalInteractivityTest(
 {
 
     [Theory]
-    [InlineData("server", true)]
-    [InlineData("webassembly", true)]
-    [InlineData("ssr", false)]
-    public void CanRenderNotFoundInteractive(string renderingMode, bool isInteractive)
+    [InlineData("server", true, false)]
+    [InlineData("webassembly", true, false)]
+    [InlineData("server", true, true)]
+    [InlineData("webassembly", true, true)]
+    [InlineData("ssr", false, true)]
+    [InlineData("ssr", false, false)]
+    public void CanRenderNotFoundPage(string renderingMode, bool isInteractive, bool useCustomNotFoundPage)
     {
-        Navigate($"/subdir/render-not-found-{renderingMode}");
+        string query = useCustomNotFoundPage ? "?useCustomNotFoundPage=true" : "";
+        Navigate($"{ServerPathBase}/render-not-found-{renderingMode}{query}");
 
         if (isInteractive)
         {
@@ -36,8 +40,16 @@ public void CanRenderNotFoundInteractive(string renderingMode, bool isInteractiv
             Browser.Exists(By.Id(buttonId)).Click();
         }
 
-        var bodyText = Browser.FindElement(By.TagName("body")).Text;
-        Assert.Contains("There's nothing here", bodyText);
+        if (useCustomNotFoundPage)
+        {
+            var infoText = Browser.FindElement(By.Id("test-info")).Text;
+            Assert.Contains("Welcome On Custom Not Found Page", infoText);
+        }
+        else
+        {
+            var bodyText = Browser.FindElement(By.TagName("body")).Text;
+            Assert.Contains("There's nothing here", bodyText);
+        }
     }
 
     [Fact]

src/Components/test/testassets/Components.WasmMinimal/Pages/CustomNotFoundPage.razor

@@ -0,0 +1,4 @@
+@page "/render-custom-not-found-page"
+
+<h3 id="test-info">Welcome On Custom Not Found Page</h3>
+<p>Sorry, the page you are looking for does not exist.</p>

src/Components/test/testassets/Components.WasmMinimal/Routes.razor

@@ -1,6 +1,28 @@
 @using Microsoft.AspNetCore.Components.Routing
+@using Components.WasmMinimal.Pages
+@inject NavigationManager NavigationManager
 
-<Router AppAssembly="@typeof(Program).Assembly">
+@code {
+    [Parameter]
+    [SupplyParameterFromQuery(Name = "useCustomNotFoundPage")]
+    public string? UseCustomNotFoundPage { get; set; }
+
+    private Type? NotFoundPageType { get; set; }
+
+    protected override void OnParametersSet()
+    {
+        if (UseCustomNotFoundPage == "true")
+        {
+            NotFoundPageType = typeof(CustomNotFoundPage);
+        }
+        else
+        {
+            NotFoundPageType = null;
+        }
+    }
+}
+
+<Router AppAssembly="@typeof(Program).Assembly" NotFoundPage="NotFoundPageType">
     <Found Context="routeData">
         <RouteView RouteData="@routeData" />
         <FocusOnNavigate RouteData="@routeData" Selector="h1" />