.net 6中得IHostingEnvironment .net provider

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:

Code
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

 

Code
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

 

Code
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

 

Code
<?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 

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