.NET Framework在web.config或app.config中默认提供了很多种设置，以便能够改变应用程序内嵌组件的行为，例如<connectionStrings>、<httpHandlers>、<sessionState>等等，这对于常规情况下的一般程序员而言是足够用的，也是非常方便的。但是我们越来越多地发现需要自己来控制一系列设置的集合 - 有时是面向组件的（自定义的或第三方提供的），有时是应用程序中使用的一系列值的集合。
.config虽然默认提供了自定义设置（在<appSettings/>节点下），但是它太弱了，仅仅只支持键值对（key/value）
<add key="myKey" value="myValue"/>
虽然键值对在大多数情况下也是很有帮助的，但是它对于健壮的组件、复杂的设置而言是不够灵活的，甚至显得过于简单。幸运的是，微软为我们提供了一种以编程的方式来访问自定义的配置/设置。
一、The Configuration Section
先看如下的配置设置，含义很明确：定义一些rss，有名字、地址、以及是否缓存
<feedRetriever>
<feeds>
<add name="cnblogs" url="http://www.cnblogs.com/rss/" />
<add name="CoolShell" url="http://coolshell.cn/rss/" cache="false" />
</feeds>
</feedRetriever>
接下来我们就以代码来展示如何调用
二、Writing the Configuration Handler
1. Representing the <add/> Element
每一个ConfigurationElement对象都是作为其内部属性（properties）集合的索引器而存在，再通过.NET提供了另一个属性（Attribute）-- 从而使得<add/>（.config中的自定义节点，取名add完全是基于微软是如此命名故为保持一致而为之）节点的attributes与FeedElement的properties进行关联（map），具体代码如下
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web; namespace WebAppCustomConfiguration
{
public class FeedElement : ConfigurationElement
{
[ConfigurationProperty("name", IsKey = true, IsRequired = true)]
public string Name
{
get { return (string)this["name"]; }
set { }
} [ConfigurationProperty("url", IsRequired = true, DefaultValue = "http://localhost")]
[RegexStringValidator(@"http?\://\S+")]
public string Url
{
get { return (string)this["url"]; }
set { }
} [ConfigurationProperty("cache", IsRequired = false, DefaultValue = true)]
public bool Cache
{
get { return (bool)this["cache"]; }
set { }
}
}
}
The following list is a complete list of possible parameters:
- DefaultValue – Gets or sets the default value for the decorated property. This parameter is not required.
- IsDefaultCollection – Gets or a sets a Boolean value indicating whether the property is the default property collection for the decorated property. This parameter is not required, and the default is false.
- IsKey – Gets or sets a Boolean value indicating whether this property is a key property for the decorated element property. This parameter is not required, and its default value is false.
- IsRequired – Gets or sets a Boolean value indicating whether the decorated element property is required. This parameter is not required, and its default value is false.
2. Writing an Element Collection Class
类ConfigurationElementCollection包含有好几个成员，但是只有两个标记为abstract，所以最简单的ConfigurationElementCollection只需实现这两个方法
- CreateNewElement() – 创建一个新的ConfigurationElement对象（本例而言就是FeedElement）；
- GetElementKey() – 获得指定配置节点的key (本例而言就是FeedElement的Name属性（property）.
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web; namespace WebAppCustomConfiguration
{
[ConfigurationCollection(typeof(FeedElement))]
public class FeedElementCollection : ConfigurationElementCollection
{
protected override ConfigurationElement CreateNewElement()
{
return new FeedElement();
} protected override object GetElementKey(ConfigurationElement element)
{
return ((FeedElement)element).Name;
}
}
}
3. Writing the FeedRetreiverSection Class
此Class较为简单，只需编程实现能够访问<feeds />节点即可，具体而言就是一属性（Property）
using System;
using System.Collections.Generic;
using System.Configuration;
using System.Linq;
using System.Web; namespace WebAppCustomConfiguration
{
public class FeedRetrieverSection : ConfigurationSection
{
[ConfigurationProperty("feeds", IsDefaultCollection = true)]
public FeedElementCollection Feeds
{
get { return (FeedElementCollection)this["feeds"]; }
set { }
}
}
}
4. Modifying web.config
下面的配置就不说了
<section name="feedRetriever" type="WebAppCustomConfiguration.FeedRetrieverSection"/>
5. Accessing Configuration Data from Code
调用的代码如下，简单不解释
using System;
using System.Collections.Generic;
using System.Configuration;
using System.IO;
using System.Linq;
using System.Net;
using System.Web; namespace WebAppCustomConfiguration
{
public class FeedRetriever
{
public static FeedRetrieverSection _Config = ConfigurationManager.GetSection("feedRetriever") as FeedRetrieverSection; public static void GetFeeds()
{
foreach (FeedElement feedElement in _Config.Feeds)
{
// make request
HttpWebRequest request = (HttpWebRequest)WebRequest.Create(feedElement.Url);
WebProxy proxy = new WebProxy("ip address:port", true);
proxy.Credentials = new NetworkCredential("username", "password", "domain");
request.Proxy = proxy;
HttpWebResponse response = (HttpWebResponse)request.GetResponse(); if (response.StatusCode == HttpStatusCode.OK)
{
string feedData = String.Empty; using (StreamReader reader = new StreamReader(response.GetResponseStream()))
{
feedData = reader.ReadToEnd();
} if (feedElement.Cache)
{
// filename of cache file
string filename = String.Format("{0}_{1}.xml", feedElement.Name, DateTime.Now.Ticks); // cache file
using (StreamWriter writer = new StreamWriter(@"D:\Deployment\Result\" + filename))
{
writer.Write(feedData);
}
}
}
}
}
}
}