格式化XML：輸出有縮進效果的XML字符串
1. 一般情況下使用以下代碼即可將XML字符串重新格式化：
        private string FormatXml(string source)
        {
            StringBuilder sb = new StringBuilder();
            XmlTextWriter writer = null;
           
            try
            {
                XmlDocument doc = new XmlDocument();
                doc.LoadXml(source);

                writer = new XmlTextWriter(new StringWriter(sb));
                writer.Formatting = Formatting.Indented;
               
                doc.WriteTo(writer);
            }
            finally
            {
                if (writer != null) writer.Close();
            }

            return sb.ToString();
        }
2. 在某些情況下如果需要對XML代碼中的Attribute也應用縮進樣式，這個時候可以通過重寫XMLTextWriter類的WriteStartAttribute方法來實現：
using System.IO;
using System.Text;
using System.Xml;

namespace Test
{
    public class XmlReformatter : XmlTextWriter
    {
        private XmlReader xr;

        private readonly StringWriter sw;

        public XmlReformatter(StringWriter sw) : base(sw)
        {
            this.sw = sw;
        }

        public override void WriteStartAttribute(string prefix, string localName, string ns)
        {
            StringBuilder sb = new StringBuilder("\r\n");

            int i = xr.Depth;

            for (i *= Indentation; i > 0; i--) sb.Append(IndentChar);

            sw.Write(sb.ToString());

            base.WriteStartAttribute(prefix, localName, ns);
        }

        public override void WriteNode(XmlReader reader, bool defattr)
        {
            xr = reader;
            base.WriteNode(reader, defattr);
        }
    }
}
調用示例：
        private string FormatXmlAttribute(string source)
        {
            StringBuilder sb = new StringBuilder();

            XmlTextReader tr = new XmlTextReader(new StringReader(source));

            XmlReformatter formatter = new XmlReformatter(new StringWriter(sb));
            formatter.Formatting = Formatting.Indented;
            formatter.WriteNode(tr, true);
            formatter.Flush();
            formatter.Close();

            tr.Close();

            return sb.ToString();
        }