Config类

using System;
using System.Xml;
using System.Collections;
using System.IO;

namespace Rocky
{
    public sealed class Config : IEnumerable
    {
        public static readonly string ConfigPath;

        static Config()
        {
            ConfigPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "Rocky.config");
        }

        private XmlNode appNode;

        public XmlNode AppNode
        {
            get { return appNode; }
        }

        public string this[string appKey]
        {
            set
            {
                lock (appNode)
                {
                    XmlElement xElem = (XmlElement)appNode.SelectSingleNode("//add[@key='" + appKey + "']");
                    if (xElem == null)
                    {
                        xElem = appNode.OwnerDocument.CreateElement("add");
                        xElem.SetAttribute("key", appKey);
                        xElem.SetAttribute("value", value);
                        appNode.AppendChild(xElem);
                    }
                    else
                    {
                        if (value == null)
                        {
                            appNode.RemoveChild(xElem);
                        }
                        else
                        {
                            xElem.SetAttribute("value", value);
                        }
                    }
                    appNode.OwnerDocument.Save(ConfigPath);
                }
            }
            get
            {
                XmlElement xElem = (XmlElement)appNode.SelectSingleNode("//add[@key='" + appKey + "']");
                if (xElem == null)
                {
                    throw new NullReferenceException();
                }
                return xElem.GetAttribute("value");
            }
        }
        public string this[int index]
        {
            set
            {
                XmlNodeList list = appNode.SelectNodes("//add");
                if (index >= 0 && index < list.Count)
                {
                    lock (appNode)
                    {
                        XmlElement xElem = (XmlElement)list[index];
                        if (value == null)
                        {
                            xElem.ParentNode.RemoveChild(xElem);
                        }
                        else
                        {
                            xElem.SetAttribute("value", value);
                        }
                        appNode.OwnerDocument.Save(ConfigPath);
                    }
                }
            }
            get
            {
                XmlNodeList list = appNode.SelectNodes("//add");
                if (index >= 0 && index < list.Count)
                {
                    return ((XmlElement)list[index]).GetAttribute("value");
                }
                throw new NullReferenceException();
            }
        }

        internal Config()
        {
            XmlDocument xDoc = new XmlDocument();
            xDoc.Load(ConfigPath);
            appNode = xDoc.SelectSingleNode("//appSettings");
            if (appNode == null)
            {
                throw new ArgumentException();
            }
        }

        public IEnumerator GetEnumerator()
        {
            return appNode.SelectNodes("//add").GetEnumerator();
        }
    }
}