XML 是可扩展标记语言（Extensible Markup Language）的缩写，其中的 标记（markup）是关键部分。你可以创建内容，然后使用限定标记标记它，从而使每个单词、短语或块成为可识别、可分类的信息。因而在C#中，对xml文件的操作尤为重要。本博客着力于在C#中如何对xml文件实施诸如创建、搜索、序列化和反序列化等操作，默认你已有一定的xml基础。
xml的基础知识可参照下面博客：
http://www.ibm.com/developerworks/cn/xml/x-newxml/
下面介绍的操作均基于Customer对象：
<Customer>
<FirstName>OrlandoFirstName>
<LastName>GeeLastName>
<EmailAddress>[email protected]EmailAddress>
Customer>一、利用C#创建xml文档
创建xml文件需要四步：
（一）新建xml文档: XmlDocument();
（二）创建根结点: CreateElement();
（三）添加子元素: AppendChild();
（四）添加元素属性: CreateElement(), AppendChild()。
首先，要使用C#中定义的操作方法，必须引入命名空间，即：
using System.Xml1、新建xml文档
XmlDocument customerXml = new XmlDocument();2、创建根结点并将其添加
XmlElement rootElem = customerXml.CreateElement("Customers");
customerXml.AppendChild(rootElem);3、添加子元素
XmlElement customerElem = customerXml.CreateElement("Customer");4、添加元素属性
XmlElement firstNameElem = customerXml.CreateElement("FirstName");
firstNameElem.InnerText = customer.FirstName;
customerElem.AppendChild(firstNameElem);5、实例代码及输出
//Create a list of customers
List customers = CreateCustomerList();
//Create a XmlDocument
XmlDocument customerXml = new XmlDocument();
//Create a root element
XmlElement rootElem = customerXml.CreateElement("Customers");
customerXml.AppendChild(rootElem);
foreach (Customer customer in customers)
{
//Create new element representing the customer object.
XmlElement customerElem = customerXml.CreateElement("Customer");
//Add element “FirstName” property to the customer element.
XmlElement firstNameElem = customerXml.CreateElement("FirstName");
firstNameElem.InnerText = customer.FirstName;
customerElem.AppendChild(firstNameElem);
//Add element: LastName property to the customer element.
XmlElement lastNameElem = customerXml.CreateElement("LastName");
lastNameElem.InnerText = customer.LastName;
customerElem.AppendChild(lastNameElem);
//Add element: EmailAddress property to the customer element.
XmlElement emailAddress = customerXml.CreateElement("EmailAddress");
emailAddress.InnerText = customer.EmailAddress;
customerElem.AppendChild(emailAddress);
//Finally add the customer element to the XML document
rootElem.AppendChild(customerElem);
}
Console.WriteLine(customerXml.OuterXml);
Console.Read(); 输出结果：
<Customers>
<Customer>
<FirstName>OrlandoFirstName>
<LastName>GeeLastName>
<EmailAddress>[email protected]EmailAddress>
Customer>
<Customer>
<FirstName>KeithFirstName>
<LastName>HarrisLastName>
<EmailAddress>[email protected]EmailAddress>
Customer>
<> …
Customers>如果想将customer的属性添加至元素表头，如：
<Customer FirstName="Orlando" LastName="Gee">
<EmailAddress>…EmailAddress>
Customer>可以使用CreateAttribute()方法:
// Add an attribute :FirstName property to the customer element.
XmlAttribute firstNameAttr = customerXml.CreateAttribute("FirstName");
firstNameAttr.Value = customer.FirstName;
customerElem.Attributes.Append(firstNameAttr);二、利用XPath在xml文件中搜索节点或属性
1.使用绝对路径搜索
XPath可以快速定位到Xml中的节点或者属性。XPath语法很简单，但是强大够用，有关其详细语法参照：
http://www.cnblogs.com/yukaizhao/archive/2011/07/25/xpath.html
搜索的结果包括两种：XmlNode与XmlEelment，其继承关系如下：
System.Object
System.Xml.XmlNode
System.Xml.XmlLinkedNode
System.Xml.XmlElement
在XmlNode类中主要用到了两个函数用来实现搜索：
SelectSingleNode(String xpath)与SelecNodes(String xpath)，差别无非是单复数的问题。
先来一段代码：
string xPath = "/Customers/Customer[@FirstName='Donna']";
XmlNode oneCustomer = customerXml.SelectSingleNode(xPath);其中第一个/表示从根节点开始搜索，第二个/就表示根节点之后的子节点了。[ ]表示搜索条件，@表示对应的属性。这样就从xml文件中搜索到了一个满足条件的xml节点。
代码示例：
string xPath = "/Customers/Customer[@FirstName='Donna']";
XmlNode oneCustomer = customerXml.SelectSingleNode(xPath);
Console.WriteLine("\nSelectSingleNode(\"{0}\")...", xPath);
if (oneCustomer != null)
Console.WriteLine(oneCustomer.OuterXml);
else
Console.WriteLine("Not found");
xPath = "/Customers/Customer[@FirstName='Donna']";
XmlElement customerElem = customerXml.SelectSingleNode(xPath) as XmlElement;
Console.WriteLine("\nSelectSingleNode(\"{0}\")...", xPath);
if (customerElem != null)
{
Console.WriteLine(customerElem.OuterXml);
Console.WriteLine("customerElem.HasAttributes = {0}", customerElem.HasAttributes);
}
else
Console.WriteLine("Not found");输出结果：
SelectSingleNode("/Customers/Customer[@FirstName='Donna']")...
"Donna" LastName="Carreras">
[email protected]
SelectSingleNode("/Customers/Customer[@FirstName='Donna']")...
"Donna" LastName="Carreras">
[email protected]
customerElem.HasAttributes = True2、使用相对路径：Axes坐标轴
如果我并不了解xml文件的构造方式，那就无法用绝对路径来搜索了，相对路径就派上用场了：
xPath = "descendant::Customer[@FirstName='Donna']";
oneCustomer = customerXml.SelectSingleNode(xPath);其中descendant表示搜索所在位置后的所有符合条件的后代，即子结点。
示例代码：
xPath = "descendant::Customer[@FirstName='Donna']";
oneCustomer = customerXml.SelectSingleNode(xPath);
Console.WriteLine("\nSelectSingleNode(\"{0}\")...", xPath);
if (oneCustomer != null)
Console.WriteLine(oneCustomer.OuterXml);
else
Console.WriteLine("Not found");输出结果：
SelectSingleNode("descendant::Customer[@FirstName='Donna']")...
"Donna" LastName="Carreras">
[email protected]
3、使用XPath函数确定条件
xPath = "descendant::Customer[starts-with(@LastName, 'G') " +
"and contains(EmailAddress, 'adventure-works.com')]";
customers = customerXml.SelectNodes(xPath);
Console.WriteLine("\nSelectNodes(\"{0}\")...", xPath);
if (customers != null)
{
foreach (XmlNode customer in customers)
Console.WriteLine(customer.OuterXml);
}
else
Console.WriteLine("Not found");常用的XPath包括：
start-with()表示传入的属性以某个字段开头//Customer[starts_with(@LastName, ‘G’)]表示取lasName以’G’打头的customer节点；
contains()表示包含第二个参数描述的属性的节点//Customer[contains(EmailAddress, ‘adventure-works.com’)]表示取EmailAddress为adventure-works.com的customer
position() 表示节点的序号例如 //cat[position() = 2] 表示取序号为2的dog节点；
last() 表示取最后一个节点 //cat[last()] ；
name() 表示当前节点名字 /pets/*[name() != ‘pig’] 表示/pets下名字不是pig的子节点。
故输出结果为：
SelectNodes("descendant::Customer[starts-with(@LastName, 'G') and contains(EmailAddress, 'adventure-works.com')]")...
"Orlando" LastName="Gee">
[email protected]
"Janet" LastName="Gates">
[email protected]
暂驻笔于此，洒家且歇歇~