Api for ASP.NET Web Application (WebForms) Project showing 400

Question

I'm new to the .NET framework and my company doesn't use Core yet, so I'm trying to figure out why my web application api is showing a 400. I had a normal web forms project and added a controller class named TagController.cs . My project is on port 44318 and I've tried accessing localhost/44318/api/tag with no luck. I also tried adding a controllers folder with api sub folder and the controller inside it, but to no avail. I've posted images of my project hierarchy and the errors themselves. I have a feeling that the project not having a global.asax could have something to do with it, but there is one in another project. Maybe TagController.cs is pointing to another port? Any help is greatly appreciated.

TagController.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Web.Http;
using ClarityDBWebFormsRedis;
using StackExchange.Redis;

namespace ClarityDBWebFormsRedis
{
    public class TagController : ApiController
    {
        // GET api/<controller>
        public IEnumerable<string> Get()
        {
            return new string[] { "value1", "value2" };
        }

        // GET api/<controller>/5
        public string Get(string data)        {
            
            return "doge";
        }

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

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

        // DELETE api/<controller>/5
        public void Delete(int id)
        {
        }
    }
}

Answer 1

You need a default (route) configuration in the project, so that it knows what it should do with the ApiControllers, or how the API can be called. This is defined for example in the Global.asax. You can simply put your class TagController into a folder called "Controllers".

The Global.asax looks then accordingly eg like this:

using System.Web.Http;
using System.Web.Routing;

(...)

protected void Application_Start(object sender, EventArgs e)
{
    RouteTable.Routes.MapHttpRoute(name: "DefaultApi", routeTemplate: "api/{controller}/{id}", defaults: new { id = RouteParameter.Optional });
}

An ApiController for example looks like this:

public class PingController : ApiController
{
    [HttpGet, AllowAnonymous]
    public IHttpActionResult Get()
    {
        return Ok();
    }
}

For normal pages it is enough to create an.Aspx page and then call it in the browser according to the created folder structure. If you use MVC, then this page is created in different files and folders in the project (Views/Home.cshtml, Models/HomeViewModel.cs and Controllers/HomeController.cs).