Writing custom Route Prefix in ASP.NET WebApi

Question

I am trying to write a custom route prefix in asp.net WebApi. Following is the class I have written (was following a book).

public class ApiVersion1RoutePrefixAttribute : RoutePrefixAttribute
 {
    private const string RouteBase = "api/{apiVersion:apiVersionConstraint(v1)}";
    private const string PrefixRouteBase = RouteBase + "/";

    public ApiVersion1RoutePrefixAttribute(string routePrefix)
        : base(string.IsNullOrWhiteSpace(routePrefix) ? RouteBase : PrefixRouteBase + routePrefix) { }

 }

When I have build the solution , I got the following Error:

"Error 1 'WebApiBook.Web.Common.Routing.ApiVersion1RoutePrefixAttribute': cannot derive from sealed type 'System.Web.Http.RoutePrefixAttribute'"

Here is my packages.config file:

Alex Art. · Accepted Answer · 2015-08-11 07:18:14Z

You are using Microsoft.AspNet.WebApi.Core version 5.0.0 which uses System.Web.Http version 5.0.0 And in this version RoutePrefixAttribute is marked as sealed so you can not extend it:

namespace System.Web.Http
{
  /// <summary>
  /// Annotates a controller with a route prefix that applies to all actions within the controller.
  /// </summary>
  [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = false)]
  public sealed class RoutePrefixAttribute : Attribute
  {
    /// <summary>
    /// Gets the route prefix.
    /// </summary>
    public string Prefix { get; private set; }

    /// <summary>
    /// Initializes a new instance of the <see cref="T:System.Web.Http.RoutePrefixAttribute"/> class.
    /// </summary>
    /// <param name="prefix">The route prefix for the controller.</param>
    public RoutePrefixAttribute(string prefix)
    {
      if (prefix == null)
        throw Error.ArgumentNull("prefix");
      this.Prefix = prefix;
    }
  }
}

Either derive from System.Web.Mvc.RoutePrefixAttribute or update your Microsoft.AspNet.WebApi.Core to latest version. Here is the implementation for version 5.2.3. As you can see the class is not selaed there:

namespace System.Web.Http
{
  /// <summary>
  /// Annotates a controller with a route prefix that applies to all actions within the controller.
  /// </summary>
  [AttributeUsage(AttributeTargets.Class, AllowMultiple = false, Inherited = true)]
  public class RoutePrefixAttribute : Attribute, IRoutePrefix
  {
    /// <summary>
    /// Gets the route prefix.
    /// </summary>
    public virtual string Prefix { get; private set; }

    /// <summary>
    /// Initializes a new instance of the <see cref="T:System.Web.Http.RoutePrefixAttribute"/> class.
    /// </summary>
    protected RoutePrefixAttribute()
    {
    }

    /// <summary>
    /// Initializes a new instance of the <see cref="T:System.Web.Http.RoutePrefixAttribute"/> class.
    /// </summary>
    /// <param name="prefix">The route prefix for the controller.</param>
    public RoutePrefixAttribute(string prefix)
    {
      if (prefix == null)
        throw Error.ArgumentNull("prefix");
      this.Prefix = prefix;
    }
  }
}

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