In ASP.NET WebApi, why is RouteData's value type "object" and not "string"

Question

In WebApi, RouteData has a Values property which is where route data is stored. For some reason, however, it implements IDictionary<string, object> rather than IDictionary<string, string>. Is the value type ever not going to be a string?

The context is that I'm writing a custom IHttpRouteConstraint to check if an integer is inside a specified range. In order to do this, I must cast my value to string and then use int.TryParse. But this will fail if the value is actually an int. Can this ever happen?

Answer 1

If you see the source code ,you'll notice Unit Tests where the value is not a string(for example BindValuesAsync_RouteData_Values_To_Simple_Types).

You said you are writing a custom constraint,let's take this one:

 public class MyConstraint : IHttpRouteConstraint
 {
       public bool Match(HttpRequestMessage request, IHttpRoute route, string parameterName, IDictionary<string, object> values, HttpRouteDirection routeDirection)
       {
            string parameters = string.Join(Environment.NewLine, values.Select(p => p.Value.GetType().FullName).ToArray());
            return true;
       }
  } 

You register it:

 config.Routes.MapHttpRoute("DefaultApi",
                                   "api/{controller}/{action}/{id}",
                                   new { id = RouteParameter.Optional }, 
                                   new { isLocal = new MyConstraint() });

Assuming you have this controller:

public class ValuesController : ApiController
{
    public string Get(int id) { return "Value"; }
}

If you make a GET request to "/api/values/Get/1" you'll notice the the values are of type

• System.String //values
• System.String //Get
• System.String //1

But

If you make a GET request to "/api/values/1" you'll notice the the values are of type

• System.String //values
• System.String //1
• System.Web.Http.RouteParameter

If you see the source code of the class

/// <summary>
/// The <see cref="RouteParameter"/> class can be used to indicate properties about a route parameter (the literals and placeholders 
/// located within segments of a <see cref="M:IHttpRoute.RouteTemplate"/>). 
/// It can for example be used to indicate that a route parameter is optional.
/// </summary>
public sealed class RouteParameter
{
    public static readonly RouteParameter Optional = new RouteParameter();

    // singleton constructor
    private RouteParameter()        {   }

    public override string ToString()   {  return string.Empty;      }
}

So, one occasion this is not a string is when you don't provide optional arguments.
You should first check the type of the object and only if it is a non empty string,try to parse it