Detect the current render mode at runtime (#32794)

aspnetcore/blazor/components/render-modes.md

@@ -5,7 +5,7 @@ description: Learn about Blazor render modes and how to apply them in Blazor Web
 monikerRange: '>= aspnetcore-8.0'
 ms.author: riande
 ms.custom: mvc
-ms.date: 02/09/2024
+ms.date: 06/10/2024
 uid: blazor/components/render-modes
 ---
 # ASP.NET Core Blazor render modes
@@ -213,6 +213,85 @@ The following example applies interactive server-side rendering (interactive SSR
 
 Additional information on render mode propagation is provided in the [Render mode propagation](#render-mode-propagation) section later in this article. The [Static SSR pages in a globally-interactive app](#static-ssr-pages-in-a-globally-interactive-app) section shows how to use the preceding approach to adopt static SSR in a globally-interactive app.
 
+:::moniker range=">= aspnetcore-9.0"
+
+## Detect rendering location, interactivity, and assigned render mode at runtime
+
+<!-- UPDATE 9.0 Renaming of API for Pre6: 
+                Update the content and remove the NOTE -->
+
+The `ComponentBase.Platform` and `ComponentBase.AssignedRenderMode` properties permit the app to detect details about the location, interactivity, and assigned render mode of a component:
+
+* `Platform.Name` returns the location where the component is executing:
+  * `Static`: On the server (SSR) and incapable of interactivity.
+  * `Server`: On the server (SSR) and capable of interactivity after prerendering.
+  * `WebAssembly`: On the client (CSR) and capable of interactivity after prerendering.
+  * `WebView`: On the native device and capable of interactivity after prerendering.
+* `Platform.IsInteractive` indicates if the component supports interactivity at the time of rendering. The value is `true` when rendering interactively or `false` when prerendering or for static SSR (`Platform.Name` of `Static`).
+* `ComponentBase.AssignedRenderMode` exposes the component's assigned render mode:
+  * `InteractiveServer` for Interactive Server.
+  * `InteractiveAuto` for Interactive Auto.
+  * `InteractiveWebassembly` for Interactive WebAssembly.
+
+> [!NOTE]
+> `ComponentBase.Platform` will be renamed to `ComponentBase.RendererInfo` in a future preview release.
+
+Components use these properties to render content depending on their location or interactivity status. For example, a form can be disabled during prerendering and enabled when the component becomes interactive:
+
+```razor
+<EditForm Model="Movie" ...>
+    <fieldset disabled="@disabled">
+        
+        ...
+
+        <button type="submit" >Save</button>
+    </fieldset>
+</EditForm>
+
+@code {
+    private bool disabled = true;
+
+    [SupplyParameterFromForm]
+    public Movie? Movie { get; set; }
+
+    protected override async Task OnInitializedAsync()
+    {
+        Movie ??= await ...;
+
+        if (Platform.IsInteractive)
+        {
+            disabled = false;
+        }
+    }
+}
+```
+
+The next example shows how to render markup to support performing a regular HTML action if the component is statically rendered:
+
+```razor
+@if (AssignedRenderMode is null)
+{
+    // The render mode is Static Server
+    <form action="/movies">
+        <input type="text" name="titleFilter" />
+        <input type="submit" value="Search" />
+    </form>
+}
+else
+{
+    // The render mode is Interactive Server, WebAssembly, or Auto.
+    <input @bind="titleFilter" />
+    <button @onclick="FilterMovies">Search</button>
+}
+```
+
+In the preceding example:
+
+* When the value of `AssignedRenderMode` is null, the component adopts static SSR. Blazor event handling isn't functional in a browser with static SSR, so the component submits a form (GET request) with a `titleFilter` query string set to the user's `<input>` value. The `Movie` component (`/movie`) can read the query string and process the value of `titleFilter` to render the component with the filtered results.
+* Otherwise, the render mode is any of `InteractiveServer`, `InteractiveWebAssembly`, or `InteractiveAuto`. The component is capable of using an event handler delegate (`FilterMovies`) and the value bound to the `<input>` element (`titleFilter`) to filter movies interactively over the background SignalR connection.
+
+:::moniker-end
+
 ## Blazor documentation examples for Blazor Web Apps
 
 When using a Blazor Web App, most of the Blazor documentation example components ***require*** interactivity to function and demonstrate the concepts covered by the articles. When you test an example component provided by an article, make sure that either the app adopts global interactivity or the component adopts an interactive render mode.