C# 2008 学习笔记 - LINQ to XML

转自：http://www.cnblogs.com/sunrack/articles/1081714.html

LINQ to XML 可以看作是一个 “better DOM” 编程模型，可以和 System.Xml.dll 程序集中的很多成员交互。

一、命名空间

System.Xml.Linq.dll 程序集定义了三个命名空间：System.Xml.Linq, System.Xml.Schema 和 System.Xml.XPath

最核心的是 System.Xml.Linq， 定义了对应 XML 文档个方面的很多类型

Member of System.Xml.Linq	Meaning in Life
XAttribute	Represents an XML attribute on a given XML element
XComment	Represents an XML comment
XDeclaration	Represents the opening declaration of an XML document
XDocument	Represents the entirety of an XML document
XElement	Represents a given element within an XML document
XName/XNamespace	Provide a very simple manner to define and reference XML namespaces

二、编程方式创建XML文档

以前的 .NET XML编程模型需要使用很多冗长的 DOM API，而 LINQ to XML 则完全可以用与 DOM 无关的方式与 XML 文档交互。这样不但大大减少了代码行，而且这种编程模型可以直接映射到格式良好的XML文档结构。

static void CreateFunctionalXmlElement()
{
// A "functional" approach to build an
// XML element in memory.
XElement inventory =
new XElement("Inventory",
new XElement("Car", new XAttribute("ID", "1"),
new XElement("Color", "Green"),
new XElement("Make", "BMW"),
new XElement("PetName", "Stan")
)
);
// Call ToString() on our XElement.
Console.WriteLine(inventory);
}

在内存中创建XML文档

static void CreateFunctionalXmlDoc()
{
XDocument inventoryDoc =
new XDocument(
new XDeclaration("1.0", "utf-8", "yes"),
new XComment("Current Inventory of AutoLot"),
new XElement("Inventory",
new XElement("Car", new XAttribute("ID", "1"),
new XElement("Color", "Green"),
new XElement("Make", "BMW"),
new XElement("PetName", "Stan")
),
new XElement("Car", new XAttribute("ID", "2"),
new XElement("Color", "Pink"),
new XElement("Make", "Yugo"),
new XElement("PetName", "Melvin")
)
)
);
// Display the document and save to disk.
Console.WriteLine(inventoryDoc);
inventoryDoc.Save("SimpleInventory.xml");
}

三、使用 LINQ 查询创建XML文档

static void CreateXmlDocFromArray()
{
// Create an anonymous array of anonymous types.
var data = new [] {
new { PetName = "Melvin", ID = 10 },
new { PetName = "Pat", ID = 11 },
new { PetName = "Danny", ID = 12 },
new { PetName = "Clunker", ID = 13 }
};
// Now enumerate over the array to build
// an XElement.
XElement vehicles =
new XElement("Inventory",
from c in data
select new XElement("Car",
new XAttribute("ID", c.ID),
new XElement("PetName", c.PetName)
)
);
Console.WriteLine(vehicles);
}

四、加载和解析XML内容

static void LoadExistingXml()
{
// Build an XElement from string.
string myElement =
@"<Car ID ='3'>
<Color>Yellow</Color>
<Make>Yugo</Make>
</Car>";
XElement newElement = XElement.Parse(myElement);
Console.WriteLine(newElement);
Console.WriteLine();
// Load the SimpleInventory.xml file.
XDocument myDoc = XDocument.Load("SimpleInventory.xml");
Console.WriteLine(myDoc);
}

六、遍历内存中的XML文档

XML示例：

<?xml version="1.0" encoding="utf-8"?>
<Inventory>
<Car carID ="0">
<Make>Ford</Make>
<Color>Blue</Color>
<PetName>Chuck</PetName>
</Car>
<Car carID ="1">
<Make>VW</Make>
<Color>Silver</Color>
<PetName>Mary</PetName>
</Car>
<Car carID ="2">
<Make>Yugo</Make>
<Color>Pink</Color>
<PetName>Gipper</PetName>
</Car>
<Car carID ="55">
<Make>Ford</Make>
<Color>Yellow</Color>
862 CHAPTER 24 n PROGRAMMING WITH THE LINQ APIS
<PetName>Max</PetName>
</Car>
<Car carID ="98">
<Make>BMW</Make>
<Color>Black</Color>
<PetName>Zippy</PetName>
</Car>
</Inventory>

加载

static void Main(string[] args)
{
Console.WriteLine("***** Fun with LINQ to XML *****/n");
// Load the Inventory.xml document into memory.
XElement doc = XElement.Load("Inventory.xml");
// We will author each of these next


PrintAllPetNames(doc);
Console.WriteLine();
GetAllFords(doc);
Console.ReadLine();
}

遍历

static void PrintAllPetNames(XElement doc)
{
var petNames = from pn in doc.Descendants("PetName")
select pn.Value;
foreach (var name in petNames)
Console.WriteLine("Name: {0}", name);
}

查询

static void GetAllFords(XElement doc)
{
var fords = from c in doc.Descendants("Make")
where c.Value == "Ford"
select c;
foreach (var f in fords)
Console.WriteLine("Name: {0}", f);
}

七、修改 XML文档

static void AddNewElements(XElement doc)
{
// Add 5 new purple Fords to the incoming document.
for (int i = 0; i < 5; i++)
{
// Create a new XElement
XElement newCar =
new XElement("Car", new XAttribute("ID", i + 1000),
new XElement("Color", "Green"),
new XElement("Make", "Ford"),
new XElement("PetName", "")
);
// Add to doc.
doc.Add(newCar);
}
// Show the updates.
Console.WriteLine(doc);
}