LinqToXml

 1 public string XmlString()
 2 {
 3     XDocument xdoc = new XDocument(
 4         new XDeclaration("1.0","UTF-8","yes"),
 5         new XElement("Root",
 6             new XElement("Child","child1"),
 7             new XElement("Child","child2"))
 8     );
 9     xdoc.Save("demo.xml");//会显示xml头声明
10     //return xdoc.ToString();//不会显示xml头声明
11     return xdoc.Declaration.ToString()+xdoc.ToString();//这样才会显示xml头声明
12 }