OpenRasta InMemoryHost that allows setting a custom resolver. Workaround for openrasta-stable issue 24

InMemoryHostWithCustomResolver.cs

using System;
using System.Linq;
using System.Reflection;
using OpenRasta.Configuration;
using OpenRasta.DI;

// ReSharper disable CheckNamespace
namespace OpenRasta.Hosting.InMemory
// ReSharper restore CheckNamespace
{
    // Hack to enable OpenRasta to use a custom IDependencyResolver.
    // See https://github.com/openrasta/openrasta-stable/issues/24
    public class InMemoryHostWithCustomResolver : InMemoryHost
    {
        // Can't pass the resolver via a constructor parameter because 
        // RaiseStart() is called before our ctor (in base ctor) - i.e.
        // resolverInstance cannot be an instance field. So it has to be 
        // a static field initialized before InMemoryHost()'s ctor is called.
        static IDependencyResolver resolverInstance;

        public InMemoryHostWithCustomResolver(IConfigurationSource configuration) : base(configuration)
        {
        }

        public static void SetResolver(IDependencyResolver resolver)
        {
            if (resolver == null) throw new ArgumentNullException("resolver");
            resolverInstance = resolver;
        }

        protected override void RaiseStart()
        {
            if (resolverInstance == null) 
                throw new InvalidOperationException("Please call SetResolver() first.");

            var resolverField = typeof(InMemoryHost)
                .GetFields(BindingFlags.NonPublic | BindingFlags.Instance)
                .Single(f => f.FieldType.Equals(typeof(IDependencyResolver)));

            resolverField.SetValue(this, resolverInstance);

            base.RaiseStart();
        }
    }
}