使用XmlReader读Xml

XmlDocument和XElement在读取Xml时要将整个Xml文档放到内存中去操作，这样做操作简单，但是很费内存和IO（可能是磁盘IO或者网络IO）；而在有些场景下我们必须考虑尽可能节省内存和IO的开销，这时候就该XmlReader和XmlWriter出场了。

XmlReader读取Xml需要通过Read()实例方法，不断读取Xml文档中的声明，节点开始，节点内容，节点结束，以及空白等等，直到文档结束，Read()方法返回false。

如下读取Xml内容实例代码和注释说明

//玉开技术博客：http://www.cnblogs.com/yukaizhao
using System;
using System.Collections.Generic;
using System.Text;
using System.Xml;
using System.IO;
 
namespace UseXmlReader
{
    class Program
    {
        static void Main(string[] args)
        {
            //声明StringReader传入Xml文本，作为XmlReader.Create的参数
            using (StringReader strRdr = new StringReader(@"<?xml version=""1.0"" encoding=""utf-8"" ?>
<root>
    <cat color=""white"">I'm a Cat</cat>
    <dog color=""yellow""/>
</root>"))
            {
                //通过XmlReader.Create静态方法创建XmlReader实例
                using (XmlReader rdr = XmlReader.Create(strRdr))
                {
                    //循环Read方法直到文档结束
                    while (rdr.Read())
                    {
                        Console.WriteLine("rdr.NodeType = " + rdr.NodeType);
                        //如果是开始节点
                        if (rdr.NodeType == XmlNodeType.Element) {
                            //通过rdr.Name得到节点名
                            string elementName = rdr.Name;
                             
                            Console.WriteLine(elementName + " element start");
                            if (elementName == "root") {
 
                            }
                            //读取到cat元素 这时rdr.Read()读取到的内容为<cat color="white">
                            else if (elementName == "cat")
                            {
                                //可以通过中括号获得属性值
                                string colorVal = rdr["color"];
                                Console.WriteLine("\tcat's color is " + colorVal);
 
                                //读取到节点内文本内容
                                if(rdr.Read()) {
                                    //通过rdr.Value获得文本内容
                                    Console.WriteLine("\t cat said:" + rdr.Value);
                                }
                            }
                        }
                        else if (rdr.NodeType == XmlNodeType.EndElement)
                        {
                            //在节点结束时也可以通过rdr.Name获得节点名字
                            string elementName = rdr.Name;
                            Console.WriteLine(elementName + " element end");
                        }
                    }
                }
            }
 
            Console.Read();
        }
    }
}