Auto load lazy property

Question

I am trying to embed a business logic implementation in a basic web API controller. Somehow, the property in the base controller is always null .

Also how can I do a lazy injection?

Startups.cs

 public IServiceProvider ConfigureServices(IServiceCollection services) { // Add framework services. services.AddMvc(); var containerBuilder = new ContainerBuilder(); containerBuilder.RegisterType<ViewBusinessLogic>().As<IViewBusinessLogic>(). PropertiesAutowired(); containerBuilder.Populate(services); var container = containerBuilder.Build(); return container.Resolve<IServiceProvider>(); } 

Interface, implementation and base controller:

 public interface IViewBusinessLogic { IEnumerable<dynamic> GetView(Guid viewId); } public class ViewBusinessLogic : BusinessLogic, IViewBusinessLogic { public IEnumerable<dynamic> GetView(Guid viewId) { return new List<dynamic> { new { Test = "Test1" }, new { Test = "Test2" } }; } } public abstract class BaseController : Controller { public IViewBusinessLogic ViewBusinessLogic { get; } } 

Answer 1

By default, controllers are not allowed by the DI framework. You need to add AddControllerAsServices so that they are enabled by the DI of your choice.

From this GitHub question :

Hi,

Maybe I'm wrong, but since I tested in depth (and checked the source code of Mvc), the controllers are not allowed from IServiceProvider , but only the constructor arguments from them are allowed with IServiceProvider .

Is it for design? I am very surprised. Because I use a different DI structure that supports property nesting. And I cannot use property nesting because Controller instances are not requested from IServiceProvider .

Have you added AddControllersAsServices to your startup ( https://github.com/aspnet/Mvc/blob/ab76f743f4ee537939b69bdb9f79bfca35398545/test/WebSites/ControllersFromServicesWebSite/Startup.cs#L37 )

The above example is cited for future reference.

 public void ConfigureServices(IServiceCollection services) { var builder = services .AddMvc() .ConfigureApplicationPartManager(manager => manager.ApplicationParts.Clear()) .AddApplicationPart(typeof(TimeScheduleController).GetTypeInfo().Assembly) .ConfigureApplicationPartManager(manager => { manager.ApplicationParts.Add(new TypesPart( typeof(AnotherController), typeof(ComponentFromServicesViewComponent), typeof(InServicesTagHelper))); manager.FeatureProviders.Add(new AssemblyMetadataReferenceFeatureProvider()); }) // This here is important .AddControllersAsServices() .AddViewComponentsAsServices() .AddTagHelpersAsServices(); services.AddTransient<QueryValueService>(); services.AddTransient<ValueService>(); services.AddSingleton<IHttpContextAccessor, HttpContextAccessor>(); } 

Regarding the second part of your question: I don't think it is possible to have a lazy instance through an IoC container. For you, it's best to create a factory class and enter factory, not a specific service.

But usually you don't need a lazy instance anyway, creating services should be fast . If this is not the case, you are probably doing some funny things in the constructor (connecting somewhere or performing other lengthy operations), which is an anti-pattern.