LINQ TO Xml【转载】

本文转载自 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<?xml:namespace prefix = o />	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);
}