ASP.NET Core 2.0 Web Api Error

I am reading trough the official tutorial from microsoft on creating an web api. https://learn.microsoft.com/en-us/aspnet/core/tutorials/first-web-api?view=aspnetcore-2.1

Now I am trying it out in visual studio and I am doing it excactly as the tutorial describes it.

But I get 2 Error: 1) The Type or Namespacename "ApiController" is not found [CS0246] 2) Type "ActionResult" is not generic and can not be used with typearguments [CS0308]

Is the tutorial out of date or why am I getting these errors?

Here is the Controller:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using TodoApi.Models;

namespace TodoApi.Controllers
{
    [Route("api/[controller]")]
    [ApiController]
    public class TodoController : ControllerBase
    {
        private TodoContext _context;

        [HttpGet]
        public ActionResult<List<TodoItem>> GetAll()
        {
            return _context.TodoItems.ToList();
        }

        [HttpGet("{id}", Name = "GetTodo")]
        public ActionResult<TodoItem> GetById(long id)
        {
            var item = _context.TodoItems.Find(id);
            if (item == null)
            {
                return NotFound();
            }
            return item;
        }

        public TodoController(TodoContext context)
        {
            _context = context;

            if(_context.TodoItems.Count() == 0)
            {
                _context.TodoItems.Add(new TodoItem { Name = "Item1" });
                _context.SaveChanges();
            }

        }        
    }
}