C# 获取 与 修改 web.config中的值（修改Xml文件）

定义web.config 中 appSettings 节点

<appSettings>
    <add key="domainExist" value="false"></add>
  </appSettings>

获取

string domainExist = ConfigurationManager.AppSettings["domainExist"];

修改并刷新

UpdAppSettings("domainExist", "true");
ConfigurationManager.RefreshSection("appSettings");

/// <summary>
    /// 修改web.config中appSettings键的值
    /// </summary>
    /// <param name="keyName">键的名称</param>
    /// <param name="keyValue">键的值</param>
    public static void UpdAppSettings( string keyName, string keyValue)
    {
        System.Xml.XmlDocument doc = new System.Xml.XmlDocument();
        try
        {
            //获取 Web.config 的路径
            string configPath = HttpRuntime.AppDomainAppPath.ToString()+"Web.config";
            doc.Load(configPath);
            System.Xml.XmlNode node;
            System.Xml.XmlElement element;
            node = doc.SelectSingleNode("//appSettings");
            element = (System.Xml.XmlElement)node.SelectSingleNode("//add[@key='" + keyName + "']");
            if (element != null)
            {
                element.SetAttribute("value", keyValue);
                doc.Save(configPath);
            }
        }
        catch (Exception)
        {
            throw;
        }

    }