自.net 2.0出世时，Provider模式就随处可见了，如：MembershipProvider、SiteMapProvider等，
它的出现使我们的应用程序有了更大的扩展性，可以是一个数据工厂的提供者，也可以是一个逻辑处理的提供者。
而实现这种模式却是相当的简单，只需实现以下四步即可：
1、定义一个类，抽象出我们所需要的操作，基类为ProviderBase
如:

public abstract class RssProvider : ProviderBase
    {
        public abstract void LoadRss();
        public abstract void AddRss();
    }

2、实现一个Section，用来从配置文件中读取Provider的相关配置，该类继承于ConfigurationSection

public class RssProviderSection : ConfigurationSection
    {
        [ConfigurationProperty("providers")]
        public ProviderSettingsCollection Providers
        {
            get { return (ProviderSettingsCollection)base["providers"]; }
            set { base["providers"] = value; }
        }

        [StringValidator(MinLength=1)]
        [ConfigurationProperty("defaultProvider", DefaultValue = "XmlProvider")]
        public string DefaultProvider
        {
            get { return (string)base["defaultProvider"]; }
            set { base["defaultProvider"] = value; }
        }
    }
    public class RssProviderCollection : ProviderCollection
    {
       //从索引器中获取指定名称的Provider
        public new RssProvider this[string name]
        {
            get
            {
                return (RssProvider)base[name];
            }
        }

        public override void Add(ProviderBase provider)
        {
            if (provider == null)
            {
                throw new ArgumentNullException("provider");
            }
            if (provider is RssProvider)
            {
                base.Add(provider);
            }
        }
    }

3、在调用时用RssProviderSection去读取配置文件，并加载指定的Provider

public class RssService
    {
        private static RssProvider _provider;
        private static RssProviderCollection _providers;
        private static readonly object obj = new object();
        public static RssProvider Provider
        {
            get
            {
                LoadProvider();
                return _provider;
            }
        }
        public static RssProviderCollection Providers
        {

            get {
                LoadProvider();
                return _providers; }
        }

        public static void LoadProvider()
        {
            if (_provider == null)
            {
                lock (obj)
                {
                    if (_provider == null)
                    {
                        RssProviderSection section = (BlogProviderSection)System.Configuration.ConfigurationManager.GetSection("Blog/RssService");
                        _providers = new RssProviderCollection();
                        ProvidersHelper.InstantiateProviders(section.Providers, _providers, typeof(BlogProvider));
                        _provider = _providers[section.DefaultProvider];
                        if (_provider == null)
                            throw new ProviderException("null");
                    }
                }
            }
        }
    }

4、配置文件

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <sectionGroup name="Blog">
      <section name="RssService" type="ClassLib.BlogProviderSection,ClassLib"/>
    </sectionGroup>
  </configSections>
  <Blog>
    <RssService defaultProvider="XmlProvider">
      <providers>
        <add name="XmlProvider" type="ClassLib.XmlProvider,ClassLib"></add>
        <add name="SqlProvider" type="ClassLib.SqlProvider,ClassLib"></add>
      </providers>
    </RssService>
  </Blog>
</configuration>

更多内容可以去MSDN查阅ProviderBase基类