REST-Api not working ControllerBase - 404 error (C# .Net Core)

Question

I'm trying to set up a Rest-API for my C# and .Net Core web application. While using the standard ASP.NET Core Web App template and adding a Controller to the package with API Controller with read/write action, I thought that the URL: https://localhost:5001/api/values would give me a response. Instead it returns an error (404).

The ValuesController.cs code:

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

// For more information on enabling Web API for empty projects, visit 
https://go.microsoft.com/fwlink/?LinkID=397860

namespace CSharp_met_database.Controllers
{
[Route("api/[controller]")]
[ApiController]
public class ValuesController : ControllerBase
{
    // GET: api/<ValuesController>
    [HttpGet]
    public IEnumerable<string> Get()
    {
        return new string[] { "value1", "value2" };
    }

    // GET api/<ValuesController>/5
    [HttpGet("{id}")]
    public string Get(int id)
    {
        return "value";
    }

    // POST api/<ValuesController>
    [HttpPost]
    public void Post([FromBody] string value)
    {
    }

    // PUT api/<ValuesController>/5
    [HttpPut("{id}")]
    public void Put(int id, [FromBody] string value)
    {
    }

    // DELETE api/<ValuesController>/5
    [HttpDelete("{id}")]
    public void Delete(int id)
    {
    }
  }
}

Maybe I'm missing something because I'm new to C# and .Net Core.

Edit

Startup.cs code:

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.HttpsPolicy;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;

namespace CSharp_met_database
{
public class Startup
{
    public Startup(IConfiguration configuration)
    {
        Configuration = configuration;
    }

    public IConfiguration Configuration { get; }

    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddRazorPages();
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();

        app.UseRouting();

        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapRazorPages();
        });
    }
  }
}

Answer 1

In your Startup.cs you are missing the controllers call in the ConfigureServices, like this:

public void ConfigureServices(IServiceCollection services)
    {
        services.AddRazorPages();
        services.AddControllers();
    }

Also missing it on the Configure method:

public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseExceptionHandler("/Error");
            // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
            app.UseHsts();
        }

        app.UseHttpsRedirection();
        app.UseStaticFiles();

        app.UseRouting();

        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapRazorPages();
            endpoints.MapControllers();
        });
    }