Loading and registering API Controllers From Class Library in ASP.NET core

Maybe you're doing something wrong. So, here are the steps to make this work.

• Create a new project: ASP.NET Core Web Application (.NET Core);
• Choose the Web API template;
• Run the project and access the "api/values" to make sure it's working;
• Add a new project to the solution named ClassLibrary: Class Library (.NET Core);
• Delete the Class1.cs and create a TestController.cs class;

• Add the MVC dependency in the project.json from the ClassLibrary project:

  "dependencies": {
    "NETStandard.Library": "1.6.0",
    "Microsoft.AspNetCore.Mvc": "1.0.0"
  },
  

• Update your TestController.cs to be like this:

  [Route("api/[controller]")]
  public class TestController : Controller{
    [HttpGet]
    public IEnumerable<string> Get() {
      return new string[] { "test1", "test2" };
    }
  }
  

• Add the reference to ClassLibrary in your WebAPI Project: right-click on "References"->"Add Reference..." or update your project.json like this:

  "dependencies": {
    "Microsoft.NETCore.App": {
      "version": "1.0.0",
      "type": "platform"
    },
    "Microsoft.AspNetCore.Mvc": "1.0.0",
    "Microsoft.AspNetCore.Server.IISIntegration": "1.0.0",
    "Microsoft.AspNetCore.Server.Kestrel": "1.0.0",
    "Microsoft.Extensions.Configuration.EnvironmentVariables": "1.0.0",
    "Microsoft.Extensions.Configuration.FileExtensions": "1.0.0",
    "Microsoft.Extensions.Configuration.Json": "1.0.0",
    "Microsoft.Extensions.Logging": "1.0.0",
    "Microsoft.Extensions.Logging.Console": "1.0.0",
    "Microsoft.Extensions.Logging.Debug": "1.0.0",
    "Microsoft.Extensions.Options.ConfigurationExtensions": "1.0.0",
    "ClassLibrary": "1.0.0-*"
  },
  

• Update your Startup.cs ConfigureServices method:

  public void ConfigureServices(IServiceCollection services) {
    services.AddMvc().AddApplicationPart(Assembly.Load(new AssemblyName("ClassLibrary")));
  }
  

• Run the project again and access "api/test";

you don't need to do anything special in Startup.cs of the main web app, it just needs to reference the class library.

The one trick is that for your controllers to be discovered your class library must directly reference MVC in its project.json file dependencies section:

"Microsoft.AspNetCore.Mvc": "1.0.*"

UPDATE: for MVC app I did not need anything special in my Startup but in one of my api apps I did need it maybe because using attribute routing.

services.AddMvc()
            .AddApplicationPart(Assembly.Load(new AssemblyName("CSharp.WebLib")))
            ;

where CSharp.WebLib is the name of my class library