A route named 'DefaultApi' is already in the route collection

问题

This question may seems duplicate but this is slightly different. In all other question in SO I had noticed that they have multiple routes registered. but in my case I have just one route.

I am creating asp.net webapi (framework 4.5) and have just one route in RegisterRoutes() method -

    public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "DefaultApi",
            url: "rest/{controller}/{id}",
            defaults: new { id = UrlParameter.Optional }
        );

    }

Then why is it throwing error?

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

回答1:

I had a similar issue with adding a route DefaultApi. Though the exact 'additional details' message in my ArgumentException stack trace was:

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

I ofcourse made sure I was adding the DefaultApi route only once, but in the end noticed that in Global.asax's Application_Start method I was calling the WebApiConfig.Register(..) twice, though in the following - not immediately obvious - way:

WebApiConfig.Register(GlobalConfiguration.Configuration);
GlobalConfiguration.Configure(WebApiConfig.Register);

Another serious case of 'copypasterites'! I simply removed the WebApiConfig.Register(..) line and that fixed my issue.

(I am using WEB API 2.0/.NET 5)

回答2:

CAUSE: renaming namespaces without removing associated bin and output files.

SOLUTION: manually delete the bin and obj folders from the output directory. (cleaning the solution is not enough, some problematic residual files remain causing this problem.)

... that was my experience anyway.

回答3:

Fine, I resolved it based on the reply by user3038092. Instead of adding it in the route collection, I added it in HttpConfiguration

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

And it worked.

回答4:

If you are using MVC4 or MVC5 application. Then put your Route Configuration in

WebApiConfig.cs and

also check route name should be unique in both files i.e RouteConfig.cs and WebApiConfig.cs

回答5:

I see that you call the controller but you do not give the controller name like this:

public static void RegisterRoutes(RouteCollection routes)
    {
        routes.IgnoreRoute("{resource}.axd/{*pathInfo}");

        routes.MapRoute(
            name: "DefaultApi",
            url: "rest/{controller}/{id}",
            defaults: new { controller="Home",action="Index",id = UrlParameter.Optional }
        );

    }

that means you regist HomeContrller for the Index view,

来源：https://stackoverflow.com/questions/20393265/a-route-named-defaultapi-is-already-in-the-route-collection