LINQ to XML

创建XML文档

 1.使用XMLDocument的方式

            XmlDocument doc = new XmlDocument();
            doc.AppendChild(doc.CreateXmlDeclaration("1.0", "utf-8", null));
            XmlElement newbook = doc.CreateElement("book");
            newbook.SetAttribute("genre", "Mystery");
            newbook.SetAttribute("publicationdate", "2001");
            newbook.SetAttribute("ISBN", "123345525");

            XmlElement newTitle = doc.CreateElement("title");
            newTitle.InnerText = "The Case of The missing cookie";
            newbook.AppendChild(newTitle);

            XmlElement newAuthor = doc.CreateElement("Author");
            newAuthor.InnerText = "James Lorain";
            newbook.AppendChild(newAuthor);
            if (doc.DocumentElement == null)
                doc.AppendChild(newbook);
            XmlTextWriter tr = new XmlTextWriter("newbook.xml", Encoding.UTF8);
            tr.Formatting = Formatting.Indented;
            doc.WriteContentTo(tr);
            tr.Close();

2.使用XDocument的方式

            XDocument xdoc = new XDocument();
            XElement root = new XElement("Book");
            xdoc.Add(root);

            XAttribute genre = new XAttribute("genre", "Mystery");
            XAttribute date = new XAttribute("publicationdate", "2001");
            XAttribute isbn = new XAttribute("ISBN", "123345525");
            root.Add(genre, date, isbn);

            XElement title = new XElement("title");
            title.Value = "The Case of The missing cookie";

            XElement author = new XElement("Author", "James Lorain");
            root.Add(title, author);

            xdoc.Save("xdoc.xml");

 2.XDocument的简洁方式

            var doc = new XDocument(new XElement("Book",
                new XAttribute("genre", "Mystery"),
                new XAttribute("publicationdate", "2002"),
                new XAttribute("ISBN", "123345525"),

                new XElement("title", "The Case of The missing cookie"),
                new XElement("Author", "James Lorain")
                )
                );
            doc.Save("xdoc2.xml");

查询

查找所有<PERSONA>元素，并且打印其值

            XDocument doc = XDocument.Load("hamlet.xml");
            doc.Descendants("PERSONA").Select(e => e.Value).ToList().ForEach(s=> {
                Console.WriteLine(s);
            }) ;

 查找<PLAY>元素下面<TILTE>元素，打印其值

<PLAY>
<TITLE>The Tragedy of Hamlet, Prince of Denmark</TITLE>

XDocument doc = XDocument.Load("hamlet.xml");
            Console.WriteLine(doc.Element("PLAY").Element("TITLE").Value);

Element("****")找到第一个符合要求的元素。

对于下面XML文件，

查找root下面长度为5的元素，打印其名称，2个属性的名称

<?xml version="1.0" encoding="utf-8"?>
<root color="red" size="large">
  <first color="red" size="medium" />
  <second color="green" size="large" />
  <third color="yellow" size="small" />
</root>

            XDocument.Load("xdoc2.xml").Root.Elements().Where(e => e.Name.ToString().Length == 5).ToList().ForEach(
                e => Console.WriteLine($"Element Name:{e.Name}, Color:{e.Attribute("color")},Size: {e.Attribute("size")}"));

结果

Element Name:first, Color:color="red",Size: size="medium"
Element Name:third, Color:color="yellow",Size: size="small"

查找属性color为green的元素，然后如上面打印

            XDocument.Load("xdoc2.xml").Root.Elements().Where(e => e.Attribute("color").Value=="green").ToList().ForEach(
                e => Console.WriteLine($"Element Name:{e.Name}, Color:{e.Attribute("color")},Size: {e.Attribute("size")}"));

 枚举Root下面的 元素，投影到新的对象集合，并且打印

            XDocument.Load("xdoc2.xml").Root.Elements().Select(e => new { name=e.Name, color = e.Attribute("color").Value })
                .ToList().ForEach(e => Console.WriteLine($"Name: {e.name} And Color {e.color}"));

结果

Name: first And Color red
Name: second And Color green
Name: third And Color yellow

修改

在元素PLAY下面的元素PERSONAE中添加一个元素PERSONA

            XElement xe = new XElement("PERSONA", "We The People");
            doc.Element("PLAY").Element("PERSONAE").Add(xe);

修改某一个元素的值

            doc.Element("PLAY").Element("PERSONAE").Element("PERSONA").SetValue("KING III");

 要保存到文件，最后需要doc.Save

一个添加节点的例子

<?xml version="1.0" encoding="utf-8"?>
<Root>
  <Student id="1">
    <name>Tom</name>
    <age>18</age>
  </Student>
  <Student id="2">
    <name>Jim</name>
    <age>20</age>
  </Student>
</Root>

要添加一个Student元素，

            var content = new XElement("Student",
                  new XAttribute("Id", "3"),
                  new XElement("name", "Jack"),
                  new XElement("age", "22"),
                  new XElement("sex", "gay")
                );
            var doc = XDocument.Load("xdoc2.xml");
            doc.Element("Root").LastNode.AddAfterSelf(content);