title: File upload .NET Core 'IFormFile' does not contain a definition for 'SaveAsASync' and no extension method
body: <p>I'm trying to upload a file using ASP.NET Core Web Api. 
  As many i found this code: </p>
  
  <pre><code>namespace ModelBindingWebSite.Controllers
  {
    public class HomeController : Controller
    {
      private IHostingEnvironment _environment;
  
      public HomeController(IHostingEnvironment environment)
      {
          _environment = environment;
      }
      public IActionResult Index()
      {
          return View();
      }
  
      [HttpPost]
      public async Task&lt;IActionResult&gt; Index(ICollection&lt;IFormFile&gt; files)
      {
          var uploads = Path.Combine(_environment.WebRootPath, "uploads");
          foreach (var file in files)
          {
              if (file.Length &gt; 0)
              {
                  var fileName = ContentDispositionHeaderValue.Parse(file.ContentDisposition).FileName.Trim('"');
                  await file.SaveAsAsync(Path.Combine(uploads, fileName));
              }
          }
          return View();
      }
  }
  </code></pre>
  
  <p>I get the error <code>IFormFile</code> does not contain a definition for <code>SaveAsASync</code> and no extension method.
  Any idea?</p>