MVC源码有关问题（关于设计模式）

/* ****************************************************************************

 *

 * Copyright (c) Microsoft Corporation. All rights reserved.

 *

 * This software is subject to the Microsoft Public License (Ms-PL). 

 * A copy of the license can be found in the license.htm file included 

 * in this distribution.

 *

 * You must not remove this notice, or any other, from this software.

 *

 * ***************************************************************************/


namespace System.Web.Mvc {

    using System;

    using System.Collections.Generic;

    using System.Collections.Specialized;

    using System.Diagnostics.CodeAnalysis;

    using System.Globalization;

    using System.Web.Mvc.Resources;


    [SuppressMessage("Microsoft.Usage", "CA2237:MarkISerializableTypesWithSerializable",

        Justification = "It is not anticipated that users will need to serialize this type.")]

    [SuppressMessage("Microsoft.Design", "CA1035:ICollectionImplementationsHaveStronglyTypedMembers",

        Justification = "It is not anticipated that users will call FormCollection.CopyTo().")]

    [FormCollectionBinder]

    public class FormCollection : NameValueCollection {


        public FormCollection() {

        }


        public FormCollection(NameValueCollection collection) {

            if (collection == null) {

                throw new ArgumentNullException("collection");

            }


            Add(collection);

        }


        public IDictionary<string, ValueProviderResult> ToValueProvider() {

            CultureInfo currentCulture = CultureInfo.CurrentCulture;


            Dictionary<string, ValueProviderResult> dict = new Dictionary<string, ValueProviderResult>(StringComparer.OrdinalIgnoreCase);

            string[] keys = AllKeys;

            foreach (string key in keys) {

                string[] rawValue = GetValues(key);

                string attemptedValue = this[key];

                ValueProviderResult vpResult = new ValueProviderResult(rawValue, attemptedValue, currentCulture);

                dict[key] = vpResult;

            }


            return dict;

        }


        public virtual ValueProviderResult GetValue(string name) {

            if (String.IsNullOrEmpty(name)) {

                throw new ArgumentException(MvcResources.Common_NullOrEmpty, "name");

            }


            string[] rawValue = GetValues(name);

            if (rawValue == null) {

                return null;

            }


            string attemptedValue = this[name];

            return new ValueProviderResult(rawValue, attemptedValue, CultureInfo.CurrentCulture);

        }


        private sealed class FormCollectionBinderAttribute : CustomModelBinderAttribute {