StringSplitFilterAttribute.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Linq;
using System.Web;
using System.Web.Mvc;

namespace Filters
{
	[AttributeUsage(AttributeTargets.Method)]
	public class SplitStringAttribute : ActionFilterAttribute
	{
		public string Parameter { get; set; }

		public string Delimiter { get; set; }

		public SplitStringAttribute()
		{
			Delimiter = ",";
		}

		public override void OnActionExecuting(ActionExecutingContext filterContext)
		{
			if (filterContext.ActionParameters.ContainsKey(this.Parameter))
			{
				string value = null;
				HttpRequestBase request = filterContext.RequestContext.HttpContext.Request;

				if (filterContext.RouteData.Values.ContainsKey(this.Parameter)
					&& filterContext.RouteData.Values[this.Parameter] is string)
				{
					value = (string)filterContext.RouteData.Values[this.Parameter];
				}
				else if (request[this.Parameter] is string)
				{
					value = request[this.Parameter] as string;
				}

				Type listArgType = GetParameterEnumerableType(filterContext);

				if (listArgType != null && !string.IsNullOrWhiteSpace(value))
				{
					string[] values = value.Split(Delimiter.ToCharArray(), StringSplitOptions.RemoveEmptyEntries);

					Type listType = typeof(List<>).MakeGenericType(listArgType);
					dynamic list = Activator.CreateInstance(listType);

					foreach (var item in values)
					{
						try
						{
							dynamic convertedValue = TypeDescriptor.GetConverter(listArgType).ConvertFromInvariantString(item);
							list.Add(convertedValue);
						}
						catch (Exception ex)
						{
							throw new ApplicationException(string.Format("Could not convert split string value to '{0}'", listArgType.FullName), ex);
						}
					}

					filterContext.ActionParameters[this.Parameter] = list;
				}
			}

			base.OnActionExecuting(filterContext);
		}

		private Type GetParameterEnumerableType(ActionExecutingContext filterContext)
		{
			var param = filterContext.ActionParameters[this.Parameter];
			Type paramType = param.GetType();
			Type interfaceType = paramType.GetInterface(typeof(IEnumerable<>).FullName);
			Type listArgType = null;

			if (interfaceType != null)
			{
				var genericParams = interfaceType.GetGenericArguments();
				if (genericParams.Length == 1)
				{
					listArgType = genericParams[0];
				}
			}

			return listArgType;
		}
	}
}