| title | author | description | ms.author | ms.date | uid |
|---|---|---|---|---|---|
Dependency injection into controllers in ASP.NET Core |
ardalis |
Discover how ASP.NET Core MVC controllers request their dependencies explicitly via their constructors with dependency injection in ASP.NET Core. |
riande |
10/13/2022 |
mvc/controllers/dependency-injection |
:::moniker range=">= aspnetcore-8.0"
By Shadi Alnamrouti and Rick Anderson
ASP.NET Core MVC controllers request dependencies explicitly via constructors. ASP.NET Core has built-in support for dependency injection (DI). DI makes apps easier to test and maintain.
View or download sample code (how to download)
Services are added as a constructor parameter, and the runtime resolves the service from the service container. Services are typically defined using interfaces. For example, consider an app that requires the current time. The following interface exposes the IDateTime service:
The following code implements the IDateTime interface:
Add the service to the service container:
For more information on xref:Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddSingleton*, see DI service lifetimes.
The following code displays a greeting to the user based on the time of day:
Run the app and a message is displayed based on the time.
The xref:Microsoft.AspNetCore.Mvc.FromServicesAttribute enables injecting a service directly into an action method without using constructor injection:
The following code shows how to access keyed services from the DI container by using the [FromKeyedServices] attribute:
:::code language="csharp" source="~/../AspNetCore.Docs.Samples/fundamentals/minimal-apis/samples/KeyServiceController/Program.cs" :::
Accessing app or configuration settings from within a controller is a common pattern. The options pattern described in xref:fundamentals/configuration/options is the preferred approach to manage settings. Generally, don't directly inject xref:Microsoft.Extensions.Configuration.IConfiguration into a controller.
Create a class that represents the options. For example:
Add the configuration class to the services collection:
Configure the app to read the settings from a JSON-formatted file:
The following code requests the IOptions<SampleWebSettings> settings from the service container and uses them in the Index method:
- See xref:mvc/controllers/testing to learn how to make code easier to test by explicitly requesting dependencies in controllers.
- Keyed service dependency injection container support
- Replace the default dependency injection container with a third party implementation.
:::moniker-end