An IRouteConstraint for ASP.NET MVC that validates a route data value to be a valid GUID.

GuidConstraint.cs

namespace Hagbarddenstore.Mvc
{
    using System;
    using System.Web;
    using System.Web.Routing;

    /// <summary>
    /// Defines the GuidConstraint type.
    /// </summary>
    public class GuidConstraint : IRouteConstraint
    {
        /// <summary>
        /// Determines whether the URL parameter contains a valid value for this constraint.
        /// </summary>
        /// <param name="httpContext">
        /// An object that encapsulates information about the HTTP request.
        /// </param>
        /// <param name="route">
        /// The object that this constraint belongs to.
        /// </param>
        /// <param name="parameterName">
        /// The name of the parameter that is being checked.
        /// </param>
        /// <param name="values">
        /// An object that contains the parameters for the URL.
        /// </param>
        /// <param name="routeDirection">
        /// An object that indicates whether the constraint check is being performed when an incoming
        /// request is being handled or when a URL is being generated.
        /// </param>
        /// <returns>
        /// <c>true</c> if the URL parameter contains a valid value; otherwise, <c>false</c>.
        /// </returns>
        public bool Match(HttpContextBase httpContext, Route route, string parameterName, RouteValueDictionary values, RouteDirection routeDirection)
        {
            object value;

            if (values.TryGetValue(parameterName, out value))
            {
                if (value is Guid)
                {
                    return true;
                }

                if (value is string)
                {
                    Guid guidValue;

                    return Guid.TryParse(value as string, out guidValue) && !Guid.Empty.Equals(guidValue);
                }
            }

            return false;
        }
    }
}