What is causing the error that swagger is already in the route collection for Web API 2? - asp.net-web-api2

Question

I installed Swagger in my ASP.Net MVC Core project and it is documenting my API beautifully.
My co-worker asked me to install it in a full framework 4.6.1 project so I've done the following.
In Package Console Manager run:
Install-Package Swashbuckle
To get your Test Web API controller working:
1) Comment this out in the WebApi.config:
// config.SuppressDefaultHostAuthentication();
// config.Filters.Add(new HostAuthenticationFilter(OAuthDefaults.AuthenticationType));
Now this URL:
http://localhost:33515/api/Test
brings back XML:
<ArrayOfstring xmlns:i="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://schemas.microsoft.com/2003/10/Serialization/Arrays">
<string>value1</string>
<string>value2</string>
</ArrayOfstring>
In Global.asax Register() I call:
SwaggerConfig.Register();
In AppStart.Swagger.Config Register() I put:
public class SwaggerConfig
{
public static void Register()
{
var thisAssembly = typeof(SwaggerConfig).Assembly;
GlobalConfiguration.Configuration
.EnableSwagger(c =>
{
c.SingleApiVersion("v1.0", "HRSA CHAFS");
c.IncludeXmlComments(GetXmlCommentsPath());
})
.EnableSwaggerUi(c =>
{});
}
private static string GetXmlCommentsPath()
{
var path = String.Format(#"{0}bin\Services.XML", AppDomain.CurrentDomain.BaseDirectory);
return path;
}
}
Now I get this error:
"A route named 'swagger_docsswagger/docs/{apiVersion}' is already in the route collection. Route names must be unique."
I've been stuck on this for hours.
How do you get rid of this?

Answer 1

This can happen when you re-name your .NET assembly. A DLL with the previous assembly name will be present in your bin folder. This causes the swagger error.
Delete your bin folder and re-build your solution.
This resolves the swagger error.

Answer 2

Swagger config uses pre-application start hook, so you don't need to call SwaggerConfig.Register() explicitly. Otherwise Register method is called twice.
[assembly: PreApplicationStartMethod(typeof(SwaggerConfig), "Register")]

Answer 3

in my case i added another project as refrence and that other project has swagger too.
i remove that refrence and move needed code to new project.

Answer 4

I solved the problem by deleting the SwaggerConfig.cs file from the App_Start folder as I had already created it manually.
Take a look at this link, here also has more useful information:
A route named 'DefaultApi' is already in the route collection error

Answer 5

In my experience the error occurs when you add reference to another project and that project is a service and it occurs on the SwaggerConfig of the referenced project. Removing project reference usually solve the problem, if you need to share classes I suggest you to create a specific project as Class Library and add its reference to both your services