description: Discover how ASP.NET Core MVC controllers request their dependencies explicitly via their constructors with dependency injection in ASP.NET Core.
By [Shadi Namrouti](https://github.com/shadinamrouti), [Rick Anderson](https://twitter.com/RickAndMSFT), and [Steve Smith](https://github.com/ardalis)
ASP.NET Core MVC controllers request dependencies explicitly via constructors. ASP.NET Core has built-in support for [dependency injection (DI)](xref:fundamentals/dependency-injection). DI makes apps easier to test and maintain.
[View or download sample code](https://github.com/dotnet/AspNetCore.Docs/tree/master/aspnetcore/mvc/controllers/dependency-injection/sample) ([how to download](xref:index#how-to-download-a-sample))
## Constructor Injection
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:
For more information on <xref:Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddSingleton*>, see [DI service lifetimes](xref:fundamentals/dependency-injection#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.
## Action injection with FromServices
The <xref:Microsoft.AspNetCore.Mvc.FromServicesAttribute> enables injecting a service directly into an action method without using constructor injection:
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:
* 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).
ASP.NET Core MVC controllers request dependencies explicitly via constructors. ASP.NET Core has built-in support for [dependency injection (DI)](xref:fundamentals/dependency-injection). DI makes apps easier to test and maintain.
[View or download sample code](https://github.com/dotnet/AspNetCore.Docs/tree/master/aspnetcore/mvc/controllers/dependency-injection/sample) ([how to download](xref:index#how-to-download-a-sample))
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:
For more information on <xref:Microsoft.Extensions.DependencyInjection.ServiceCollectionServiceExtensions.AddSingleton*>, see [DI service lifetimes](xref:fundamentals/dependency-injection#service-lifetimes).
The <xref:Microsoft.AspNetCore.Mvc.FromServicesAttribute> enables injecting a service directly into an action method without using constructor injection:
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.
* [Replace the default dependency injection container with a third party implementation](xref:fundamentals/dependency-injection#default-service-container-replacement).
