Add AddControllersAsServices documentation to DI into controllers article

aspnetcore/mvc/controllers/dependency-injection.md

@@ -1,9 +1,10 @@
 ---
 title: Dependency injection into controllers in ASP.NET Core
+ai-usage: ai-assisted
 author: ardalis
 description: Discover how ASP.NET Core MVC controllers request their dependencies explicitly via their constructors with dependency injection in ASP.NET Core.
 ms.author: tdykstra
-ms.date: 10/13/2022
+ms.date: 03/02/2026
 uid: mvc/controllers/dependency-injection
 ---
 # Dependency injection into controllers in ASP.NET Core
@@ -71,6 +72,27 @@ The following code requests the `IOptions<SampleWebSettings>` settings from the
 
 [!code-csharp[](~/mvc/controllers/dependency-injection/3.1sample/ControllerDI/Controllers/SettingsController.cs?name=snippet)]
 
+## Controllers as services
+
+By default, ASP.NET Core doesn't register controllers as services in the DI container. The runtime uses the [DefaultControllerActivator](https://source.dot.net/#Microsoft.AspNetCore.Mvc.Core/Controllers/DefaultControllerActivator.cs) to create controller instances and resolves services from the DI container for constructor parameters, but the controller itself isn't resolved from the container.
+
+Calling `AddControllersAsServices` registers all controllers as services in the DI container:
+
+```csharp
+var builder = WebApplication.CreateBuilder(args);
+
+builder.Services.AddControllersWithViews().AddControllersAsServices();
+```
+
+Registering controllers as services enables:
+
+* Intercepting controller creation with a custom `IControllerActivator`.
+* Using any DI lifetime management for controllers.
+* Injecting services into controllers using any registered constructor, since the DI container selects the constructor.
+
+> [!NOTE]
+> Configure the `ApplicationPartManager` **before** calling `AddControllersAsServices`. See <xref:mvc/extensibility/app-parts#prevent-loading-resources> for details.
+
 ## Additional resources
 
 * See <xref:mvc/controllers/testing> to learn how to make code easier to test by explicitly requesting dependencies in controllers.

aspnetcore/mvc/controllers/includes/dependency-injection7.md

@@ -55,6 +55,28 @@ The following code requests the `IOptions<SampleWebSettings>` settings from the
 
 [!code-csharp[](~/mvc/controllers/dependency-injection/3.1sample/ControllerDI/Controllers/SettingsController.cs?name=snippet)]
 
+## Controllers as services
+
+By default, ASP.NET Core doesn't register controllers as services in the DI container. The runtime uses the [DefaultControllerActivator](https://source.dot.net/#Microsoft.AspNetCore.Mvc.Core/Controllers/DefaultControllerActivator.cs) to create controller instances and resolves services from the DI container for constructor parameters, but the controller itself isn't resolved from the container.
+
+Calling `AddControllersAsServices` registers all controllers as services in the DI container:
+
+```csharp
+public void ConfigureServices(IServiceCollection services)
+{
+    services.AddControllersWithViews().AddControllersAsServices();
+}
+```
+
+Registering controllers as services enables:
+
+* Intercepting controller creation with a custom `IControllerActivator`.
+* Using any DI lifetime management for controllers.
+* Injecting services into controllers using any registered constructor, since the DI container selects the constructor.
+
+> [!NOTE]
+> Configure the `ApplicationPartManager` **before** calling `AddControllersAsServices`. See <xref:mvc/extensibility/app-parts#prevent-loading-resources> for details.
+
 ## Additional resources
 
 * See <xref:mvc/controllers/testing> to learn how to make code easier to test by explicitly requesting dependencies in controllers.
@@ -117,10 +139,33 @@ The following code requests the `IOptions<SampleWebSettings>` settings from the
 
 [!code-csharp[](~/mvc/controllers/dependency-injection/sample/ControllerDI/Controllers/SettingsController.cs?name=snippet)]
 
+## Controllers as services
+
+By default, ASP.NET Core doesn't register controllers as services in the DI container. The runtime uses the [DefaultControllerActivator](https://source.dot.net/#Microsoft.AspNetCore.Mvc.Core/Controllers/DefaultControllerActivator.cs) to create controller instances and resolves services from the DI container for constructor parameters, but the controller itself isn't resolved from the container.
+
+Calling `AddControllersAsServices` registers all controllers as services in the DI container:
+
+```csharp
+public void ConfigureServices(IServiceCollection services)
+{
+    services.AddMvc().AddControllersAsServices();
+}
+```
+
+Registering controllers as services enables:
+
+* Intercepting controller creation with a custom `IControllerActivator`.
+* Using any DI lifetime management for controllers.
+* Injecting services into controllers using any registered constructor, since the DI container selects the constructor.
+
+> [!NOTE]
+> Configure the `ApplicationPartManager` **before** calling `AddControllersAsServices`. See <xref:mvc/extensibility/app-parts#prevent-loading-resources> for details.
+
 ## Additional resources
 
 * See <xref:mvc/controllers/testing> to learn how to make code easier to test by explicitly requesting dependencies in controllers.
 
 * [Replace the default dependency injection container with a third party implementation](xref:fundamentals/dependency-injection#default-service-container-replacement).
 
 :::moniker-end
+