InvalidCastException When Attribute-Routed Controllers Have the Same Name

[commonsensesoftware]

Synopsis

When versioned controllers that use attribute routing with the same name, but in different namespaces, an InvalidCastException is thrown.

For example:

namespace Example.V1
{
    [ApiVersion( "1.0" )]
    [Route( "api/helloworld" )]
    public class HelloWorldController : ApiController { /* omitted */ }
}
namespace Example.V2
{
    [ApiVersion( "2.0" )]
    [Route( "api/helloworld" )]
    public class HelloWorldController : ApiController { /* omitted */ }
}
namespace Example.V3
{
    [ApiVersion( "3.0" )]
    [Route( "api/helloworld" )]
    public class HelloWorldController : ApiController { /* omitted */ }
}

Analysis

This behavior occurs because although the correct controller type is selected, the action binding is paired to a method from the incorrect candidate controller. For example, api/helloworld?api-version=3.0 selects Example.V3.HelloWorldController, but binds the action to Example.V1.HelloWorldController.Get. This behavior only appears to manifest for attribute-routed controllers and only if the controllers also have the same name.