C#探秘系列（七）（XML文件操作（一）） c#

【C#探秘系列（七）（XML文件操作（一））】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：

Orlando Gee orlando0@hotmail.com

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.Xml

1、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 propertyto 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：

Orlando Gee orlando0@hotmail.com Keith Harris keith0@hotmail.com <> …

如果想将customer的属性添加至元素表头，如：

…

可以使用CreateAttribute()方法:

// Add an attribute :FirstName propertyto the customer element. XmlAttribute firstNameAttr = customerXml.CreateAttribute("FirstName"); firstNameAttr.Value = https://www.it610.com/article/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']")... donna0@adventure-works.com SelectSingleNode("/Customers/Customer[@FirstName='Donna']")... donna0@adventure-works.com customerElem.HasAttributes = True

2、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']")... donna0@adventure-works.com

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')]")... orlando0@adventure-works.com janet1@adventure-works.com

暂驻笔于此，洒家且歇歇~
转载于:https://www.cnblogs.com/jscitlearningshare/p/4457937.html