Converter.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SimpleTest.Tdd
{
    internal interface IConverter
    {
        object Convert(List<string> values);
    }

    internal class KeywordConverter : IConverter
    {
        public object Convert(List<string> values)
        {
            return values[0];
        }
    }

    internal class PriceRangeConverter : IConverter
    {
        public object Convert(List<string> values)
        {
            return new PriceRange
            {
                Min = float.Parse(values[0]),
                Max = float.Parse(values[1])
            };
        }
    }

    internal class ColorConverter : IConverter
    {
        public object Convert(List<string> values)
        {
            return null;
        }
    }
}

SearchCriteria.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SimpleTest.Tdd
{
    public class SearchCriteria
    {
        public PriceRange Price { get; set; }
        public string Keywords { get; set; }
        public Color Colors { get; set; }
    }

    [Flags]
    public enum Color
    { 
        Red = 1,
        Black = 1 << 1,
        White = 1 << 2
    }

    public class PriceRange
    {
        public float Min { get; set; }
        public float Max { get; set; }
    }
}

SearchCriteriaBinder.cs

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

namespace SimpleTest.Tdd
{
    public class SearchCriteriaBinder : IModelBinder
    {
        public SearchCriteriaBinder()
            : this(new Tokenizer(), new SearchCriteriaBuilder()) { }

        internal SearchCriteriaBinder(ITokenizer tokenizer, ISearchCriteriaBuilder builder)
        {
            this.m_tokenizer = tokenizer;
            this.m_builder = builder;
        }

        private readonly ITokenizer m_tokenizer;
        private readonly ISearchCriteriaBuilder m_builder;

        public object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
        {
            var modelName = bindingContext.ModelName;
            var rawValue = bindingContext.ValueProvider[modelName].RawValue;

            var text = HttpUtility.UrlDecode(rawValue.ToString());
            var tokenGroups = this.m_tokenizer.Tokenize(text);

            return this.m_builder.Build(tokenGroups);
        }
    }
}

SearchCriteriaBuilder.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SimpleTest.Tdd
{
    internal interface ISearchCriteriaBuilder
    {
        SearchCriteria Build(List<string[]> tokenGroups);
    }

    internal class SearchCriteriaBuilder : ISearchCriteriaBuilder
    {
        internal SearchCriteriaBuilder() : this(GetConverter)
        {
        }

        internal SearchCriteriaBuilder(Func<string, IConverter> converterGetter)
        {
            this.m_getConverter = converterGetter;
        }

        internal static IConverter GetConverter(string field)
        {
            // 使用if ... else或是字典
            return null;
        }

        private readonly Func<string, IConverter> m_getConverter;

        public SearchCriteria Build(List<string[]> tokenGroups)
        {
            var fieldTokens = tokenGroups.ToDictionary(
                g => g[0].ToLowerInvariant(),
                g => g.Skip(1).ToList());

            var searchCriteria = new SearchCriteria();

            List<string> values;
            if (fieldTokens.TryGetValue("keywords", out values))
            {
                searchCriteria.Keywords = (string)this.m_getConverter("keywords").Convert(values);
            }

            if (fieldTokens.TryGetValue("price", out values))
            {
                searchCriteria.Price = (PriceRange)this.m_getConverter("price").Convert(values);
            }

            if (fieldTokens.TryGetValue("color", out values))
            {
                searchCriteria.Colors = (Color)this.m_getConverter("color").Convert(values);
            }

            return searchCriteria;
        }
    }
}

Tokenizer

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace SimpleTest.Tdd
{
    internal interface ITokenizer
    {
        List<string[]> Tokenize(string text);
    }

    internal class Tokenizer : ITokenizer
    {
        public List<string[]> Tokenize(string text)
        {
            return null;
        }
    }
}