Implements IConfigurationSectionHandler interface,create a custom configuration section handler

最新推荐文章于 2023-04-24 14:05:12 发布

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本文探讨了在配置文件中使用自定义配置节处理器实现多值存储的方法，解决了单值覆盖的问题，并提供了相应的代码实现和优化建议。

原帖地址:应用程序配置文件问题

配置文件如下:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="RinexHeader" type="System.Configuration.NameValueSectionHandler"/>
  </configSections>
  <RinexHeader>
    <!--O文件文件头标签字符串集合，和OHeaderLabel中的枚举值要一一对应-->
    <add key="OHeadLabel" value="RINEX VERSION / TYPE"/>
    <add key="OHeadLabel" value="PGM / RUN BY / DATE"/>
    <add key="OHeadLabel" value="COMMENT"/>
  </RinexHeader>
</configuration>

文中网友使用 NameValueSectionHandler 来处理 configuration section，他的问题是为什么 OHeadLabel 只取到一个，而不是多个。

这里要说明一下， NameValueSectionHandler 在处理 configuration section 的时候，使用的方式是

ReadOnlyNameValueCollectionInstance[key] = value;

这样相同 key 只会保留最后一个，之前的都会被覆盖掉。

所以在这里 NameValueSectionHandler 是不能胜任的。

还要说明下 NameValueSectionHandler 和 DictionarySectionHandler 除了在 GetSection 时返回类型不同外，基本相同。

因为 DictionarySectionHandler 返回的是哈希表，所以在大量节点的情况下后续查找的速度会比 NameValueSectionHandler 快。

为了实现需求，我们可以自定义 configuration section handler

思路很简单，在原本返回单个节点的属性值的地方返回集合。

具体代码如下:

public class CustomSectionHandler : IConfigurationSectionHandler
    {
        #region IConfigurationSectionHandler Members
        
        object IConfigurationSectionHandler.Create(
  object parent, object configContext, XmlNode section)
        {
            // Creates the configuration object that this method will return.
            // This can be a custom configuration class.
            // In this example, we use a System.Collections.Generic.IDictionary<string, IList<string>>.

            IDictionary<string, IList<IDictionary<string, string>>> myConfigObject = new Dictionary<string, IList<IDictionary<string, string>>>();

            // Gets any attributes for this section element.
            IDictionary<string, string> myAttribs = new Dictionary<string, string>();

            foreach (XmlAttribute attrib in section.Attributes)
            {
                if (XmlNodeType.Attribute == attrib.NodeType)
                    myAttribs.Add(attrib.Name, attrib.Value);
            }

            IList<IDictionary<string, string>> list = new List<IDictionary<string, string>>();

            // Puts the section name and attributes as the first config object item.
            list.Add(myAttribs);
            myConfigObject.Add(section.Name, list);

            // Gets the child element names and attributes.            
            foreach (XmlNode child in section.ChildNodes)
            {
                if (XmlNodeType.Element == child.NodeType)
                {
                    IDictionary<string, string> myChildAttribs = new Dictionary<string, string>();

                    foreach (XmlAttribute childAttrib in child.Attributes)
                    {
                        if (XmlNodeType.Attribute == childAttrib.NodeType)
                            myChildAttribs.Add(childAttrib.Name, childAttrib.Value);
                    }
                    if (myConfigObject.ContainsKey(myChildAttribs["key"]))
                    {
                        myConfigObject[myChildAttribs["key"]].Add(myChildAttribs);
                    }
                    else
                    {
                        list = new List<IDictionary<string, string>>();
                        list.Add(myChildAttribs);
                        myConfigObject.Add(myChildAttribs["key"], list);
                    }
                }
            }
            return (myConfigObject);
        }
        #endregion
    }

设置config

<configSections>
     <section name="RinexHeader" type="namespace.CustomSectionHandler,namespace, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"/>
</configSections>

调用代码

IDictionary<string, IList<IDictionary<string, string>>> dic = System.Configuration.ConfigurationManager.GetSection("RinexHeader") as Dictionary<string, IList<IDictionary<string, string>>>;

            if (dic.ContainsKey("OHeadLabel"))
            {
                foreach (var v in dic["OHeadLabel"])
                {
                    Console.WriteLine(v["value"]);
                }
            }

虽然实现了功能，但也暴露了问题 if (myConfigObject.ContainsKey(myChildAttribs["key"])) 可以看到 key 是硬编码在这的，这并不是一个好的实现。

而且配置文件中

<add key="OHeadLabel" value="RINEX VERSION / TYPE"/>
<add key="OHeadLabel" value="PGM / RUN BY / DATE"/>
<add key="OHeadLabel" value="COMMENT"/>

add 毫无意义，所以应改成

<OHeadLabel value="RINEX VERSION / TYPE"/>
<OHeadLabel value="PGM / RUN BY / DATE"/>
<OHeadLabel value="COMMENT"/>

然后修改之前的程序，myChildAttribs["key"] => child.Name

修改后的代码:

 public class CustomSectionHandler : IConfigurationSectionHandler
    {
        #region IConfigurationSectionHandler Members

        object IConfigurationSectionHandler.Create(
  object parent, object configContext, XmlNode section)
        {
            // Creates the configuration object that this method will return.
            // This can be a custom configuration class.
            // In this example, we use a System.Collections.Generic.IDictionary<string, IList<string>>.

            IDictionary<string, IList<IDictionary<string, string>>> myConfigObject = new Dictionary<string, IList<IDictionary<string, string>>>();

            // Gets any attributes for this section element.
            IDictionary<string, string> myAttribs = new Dictionary<string, string>();

            foreach (XmlAttribute attrib in section.Attributes)
            {
                if (XmlNodeType.Attribute == attrib.NodeType)
                    myAttribs.Add(attrib.Name, attrib.Value);
            }

            IList<IDictionary<string, string>> list = new List<IDictionary<string, string>>();

            // Puts the section name and attributes as the first config object item.
            list.Add(myAttribs);
            myConfigObject.Add(section.Name, list);

            // Gets the child element names and attributes.            
            foreach (XmlNode child in section.ChildNodes)
            {
                if (XmlNodeType.Element == child.NodeType)
                {
                    IDictionary<string, string> myChildAttribs = new Dictionary<string, string>();

                    foreach (XmlAttribute childAttrib in child.Attributes)
                    {
                        if (XmlNodeType.Attribute == childAttrib.NodeType)
                            myChildAttribs.Add(childAttrib.Name, childAttrib.Value);
                    }
                    if (myConfigObject.ContainsKey(child.Name))
                    {
                        myConfigObject[child.Name].Add(myChildAttribs);
                    }
                    else
                    {
                        list = new List<IDictionary<string, string>>();
                        list.Add(myChildAttribs);
                        myConfigObject.Add(child.Name, list);
                    }
                }
            }
            return (myConfigObject);
        }
        #endregion
    }

大功告成。