This post describes one of the changes to Startup when moving from an ASP.NET Core 2.x app to .NET Core 3; you can no longer inject arbitrary services into the Startup constructor.

In many cases, you’ll want to ship MVC controllers, possibly views or tag helpers, etc… as part of your class library. To do this correctly you’ll want to add your assembly to ASP.NET’s “Application Parts” on startup. Its quite simple to do but you might want to make sure you are not enabling all sorts of services that the user of your library doesn’t need.

DI will help us to simplify the management of all our dependencies. Services are registered in the net core container specifically in the Startup class. The container is responsible for creating and disposing of all service instances or in other words, it’s responsible for the life-time of all services registering in.

You have probably wondered whether it is possible to manipulate different instances of the same service according to a certain context in your application. Well, know that it is possible. I have prepared in this article a concrete example of dynamic dependency injection in a multitenant WebAPI context: for the same service (interface) it is possible to invoke the concrete instance appropriate for the current tenant.

We all probably know how to inject an instance of the interface to the class using dependency injection in ASP.NET Core. But how can we inject all instances of the interface to some class, let’s say, controller, using dependency injection? The trick is simple and it’s shown in this blog post.