Error - An exception of type 'System.ArgumentException' occurred in System.Web.dll but was not handled in user code

Question

User-797751191 posted

Hi

An exception of type 'System.ArgumentException' occurred in System.Web.dll but was not handled in user code

Additional information: A route named 'DefaultApi' is already in the route collection. Route names must be unique.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web.Http;
using System.Net.Http.Headers;


namespace WebApi
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services

            // Web API routes
            //config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );

            config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
        }


    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;

namespace WebApi
{
    public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            WebApiConfig.Register(GlobalConfiguration.Configuration);
            AreaRegistration.RegisterAllAreas();
            GlobalConfiguration.Configure(WebApiConfig.Register);
            //FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            //RouteConfig.RegisterRoutes(RouteTable.Routes);
            //BundleConfig.RegisterBundles(BundleTable.Bundles);
        }
    }
}

Thanks

Answer 1

User475983607 posted

The error is very clear.   You have two Controllers/Actions with the same route name.   Can you share the relevant controller(s) and/or configuration?  Global.asax?

Answer 2

User-719153870 posted

Hi jsshivalik,

A route named 'DefaultApi' is already in the route collection. Route names must be unique.

WebApiConfig.Register(GlobalConfiguration.Configuration);

GlobalConfiguration.Configure(WebApiConfig.Register);

It seems you called the Register twice that caused thie error. Please comment out one of them and uncomment the last three lines of code in your Global.asax.cs.

Please refer to A route named 'DefaultApi' is already in the route collection and below code:

WebApiConfig.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http.Headers;
using System.Web.Http;

namespace WebApiDemo01
{
    public static class WebApiConfig
    {
        public static void Register(HttpConfiguration config)
        {
            // Web API configuration and services

            // Web API routes
            //config.MapHttpAttributeRoutes();

            config.Routes.MapHttpRoute(
                name: "DefaultApi",
                routeTemplate: "api/{controller}/{id}",
                defaults: new { id = RouteParameter.Optional }
            );
            config.Formatters.JsonFormatter.SupportedMediaTypes.Add(new MediaTypeHeaderValue("text/html"));
        }
    }
}

Global.asax.cs:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Http;
using System.Web.Mvc;
using System.Web.Optimization;
using System.Web.Routing;

namespace WebApiDemo01
{
    public class WebApiApplication : System.Web.HttpApplication
    {
        protected void Application_Start()
        {
            WebApiConfig.Register(GlobalConfiguration.Configuration);//you can comment this line out

            AreaRegistration.RegisterAllAreas();
            //GlobalConfiguration.Configure(WebApiConfig.Register);//Or this line
            FilterConfig.RegisterGlobalFilters(GlobalFilters.Filters);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            BundleConfig.RegisterBundles(BundleTable.Bundles);
        }
    }
}

Best Regard,

Yang Shen