XmlDocument和XDocument转String

1：XDocument转String直接使用ToString();XNode里面重写了ToString()方法

2：XmlDocument转String需要写代码

 using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Text;
 using System.Threading.Tasks;
 using System.Xml;
 using System.Xml.Linq;
 using System.IO;

 namespace XmlToString
 {
     class Program
     {
         static void Main(string[] args)
         {
             var xDoc = new XDocument(
                 new XElement("root111",
                     new XElement("dog",
                         new XText("哈哈哈"),
                         new XAttribute("color", "black")
                         ),
                     //new XElement("cat"),
                     new XElement("pig", "pig is great")
                 ));
             Console.WriteLine(xDoc.ToString());
             string strXml = "<?xml version=\"1.0\" encoding=\"utf-8\"?><books><book>1</book><book>2</book><book>3</book><book>4</book></books>";
             XmlDocument xx = new XmlDocument();
             xx.LoadXml(strXml);
             Console.WriteLine(xx.ToString());
             StringWriter sw = new StringWriter();
             XmlTextWriter xmlTextWriter = new XmlTextWriter(sw);
             xx.WriteTo(xmlTextWriter);
             Console.WriteLine(sw.ToString());
             Console.ReadKey();
         }
     }
 }