.net中的Provider模式 [转帖]

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();  
    }  

 

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);  
            }  
        }  
    }  
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");  
                    }  
                }  
            }  
        }  
    }  
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>  
<?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

转自：http://www.yibin001.com/Archives/6024.aspx