title: ApiController not found in .NET Core WebApi project
body: <p>I have created a new .NET Core WebAPI project in Visual Studio Code.  All dependencies have been restored.   The project is using the following SDK and runtimes:</p>
  
  <ul>
  <li>.NET Core SDK 2.1.302</li>
  <li>Microsoft.AspNetCore.All 2.1.2 </li>
  <li>Microsoft.AspNetCore.App 2.1.2</li>
  <li>Microsoft.NETCore.App 2.1.2 </li>
  </ul>
  
  <p>My controller class (including a screenshot for the Intellisense view):</p>
  
  <pre><code>using Microsoft.AspNetCore.Mvc;
  using System.Collections.Generic;
  using System.Linq;
  
  namespace Gmn.Controllers
  {
      [Route("api/[controller]")]
      [ApiController]
      public class MyController : ControllerBase
      {
          public MyController() {
  
          }
      }
  }
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/uB7WX.png" rel="noreferrer"><img src="https://i.stack.imgur.com/uB7WX.png" alt="Syntax highlighting shows ApiController not found"></a></p>
  
  <p>Build error:</p>
  
  <blockquote>
    <p>error CS0246: The type or namespace name 'ApiControllerAttribute'
    could not be found (are you missing a using directive or an assembly
    reference?)</p>
  </blockquote>
  
  <p>The <code>Route</code> attribute, which is also in the Microsoft.AspNetCore.Mvc assembly, resolves correctly, no error.  So, I know the assembly is present.</p>
  
  <p>Per MS Docs, the attribute is defined in this assembly:</p>
  
  <p><a href="https://i.stack.imgur.com/mmgwp.png" rel="noreferrer"><img src="https://i.stack.imgur.com/mmgwp.png" alt="MS Docs for ApiControllerAttribute"></a></p>
  
  <p>After 3 hours of searching I have not been able to figure this out.  I'm new to .NET Core, but not .NET.</p>
  
  <p>Any suggestions how to resolve this issue?   Thanks.</p>