假设xml文件内容是

<?xml version="1.0" encoding="utf-8"?>
<Workflow>
  <Activity>
    <ActivityId>1</ActivityId>
    <ActivityName>start</ActivityName>
    <BindingPageId>1</BindingPageId>
    <BindingRoleId>1</BindingRoleId>
    <ActivityLevel>1</ActivityLevel>
  </Activity>
  <Activity>
    <ActivityId>2</ActivityId>
    <ActivityName>pass</ActivityName>
    <BindingPageId>2</BindingPageId>
    <BindingRoleId>2</BindingRoleId>
    <ActivityLevel>2</ActivityLevel>
  </Activity>
</Workflow>

我们需要读取Activity节点下的内容，因为存在多个Activity，所以需要读取多个节点。可以使用 XmlDocument.SelectSingleNode和XmlDocument.SelectNodes方法查找节点。前一个是查找匹配的第一个节 点，而后一个则会返回一个节点列表。

1.XmlDocument.SelectSingleNode方法的使用

首先创建一个读取xml文件的方法ReadXmlNode

/// <summary>  
        /// 读取xml中的指定节点的值
        /// </summary>  
        public void ReadXmlNode(string filename)
        {
            XmlDocument xmlDoc = new XmlDocument();
            try
            {
                xmlDoc.Load(filename);
                //读取Activity节点下的数据。SelectSingleNode匹配第一个Activity节点
                XmlNode root = xmlDoc.SelectSingleNode("//Activity");//当节点Workflow带有属性是，使用SelectSingleNode无法读取        
                if (root != null)
                {
                    string ActivityId = (root.SelectSingleNode("ActivityId")).InnerText;
                    string ActivityName = (root.SelectSingleNode("ActivityName ")).InnerText;
                    string ActivityLevel = root.SelectSingleNode("ActivityLevel").InnerText;
                    Console.WriteLine("ActivityId:" + ActivityId + "/nActivityName:" + ActivityName + "/nActivityLevel:" + ActivityLevel);
                }
                else
                {
                    Console.WriteLine("the node  is not existed");
                    //Console.Read();
                }
            }
            catch (Exception e)
            {
                //显示错误信息
                Console.WriteLine(e.Message);
            }
        }

然后在主函数中调用该方法

class Program
    {
        static void Main(string[] args)
        {
            XMLOperation xmlOpr = new XMLOperation();
            xmlOpr.ReadXmlNode("activity.xml");
            Console.Read();
        }
    }

输出结果为：

ActivityId:1
ActivityName:start
ActivityLevel:1

2.XmlDocument.SelectNodes方法的使用

/// <summary>  
        /// 读取xml中的指定节点的值，如果有多个同名节点，则全部读取
        /// </summary>  
        public void ReadXmlNodes(string filename)
        {
            XmlDocument xmlDoc = new XmlDocument();
            try
            {
                xmlDoc.Load(filename);
                XmlNodeList xnList = xmlDoc.SelectNodes("//Activity");
                Console.WriteLine("共有{0}个节点", xnList.Count);//输出xnList中节点个数。
                foreach (XmlNode xn in xnList)
                {
                    //无法使用xn["ActivityId"].InnerText
                    string ActivityId = (xn.SelectSingleNode("ActivityId")).InnerText;
                    string ActivityName = xn.SelectSingleNode("ActivityName").InnerText;
                    string ActivityLevel = xn.SelectSingleNode("ActivityLevel").InnerText;
                    //  Console.WriteLine("ActivityId:" + ActivityId + "/nActivityName:" + ActivityName + "/nActivityLevel:" + ActivityLevel);
                    Console.WriteLine("ActivityId:  {0}/nActivityName:  {1}/nActivityLevel:  {2}", ActivityId, ActivityName, ActivityLevel);
                }
            }
            catch (Exception e)
            {
                //显示错误信息
                Console.WriteLine(e.Message);
            }
        }

然后在主函数中调用该方法

class Program
    {
        static void Main(string[] args)
        {
            XMLOperation xmlOpr = new XMLOperation();
            xmlOpr.ReadXmlNodes("activity.xml");
            Console.Read();
        }
    }

输出结果为：

共有2个节点
ActivityId:  1
ActivityName:  start
ActivityLevel:  1
ActivityId:  2
ActivityName:  pass
ActivityLevel:  2

3.通过节点属性查找指定节点

参考http://www.csharp-examples.net/xml-nodes-by-attribute-value/，虽然没有用到参考文章中的方法，不过总觉得以后会用到的。

/// <summary>  
        ///通过ActivityLevel获取xmlnode，需要保证ActivityLevel在一个xml文档中是唯一的。
        /// </summary>  
        public XmlNode getXmlNode(string filename, string activitylevel)
        {
            XmlDocument xmlDoc = new XmlDocument();
            try
            {
                xmlDoc.Load(filename);
                XmlNodeList xnList = xmlDoc.SelectNodes("//Activity");//当节点Workflow带有属性是，使用SelectSingleNode无法读取        
                foreach (XmlNode xn in xnList)
                {
                    string ActivityLevel = xn.SelectSingleNode("ActivityLevel").InnerText;
                    if(activitylevel==ActivityLevel)
                    {
                        return xn;
                    }
                }
            }
            catch (Exception e)
            {
                //显示错误信息
                Console.WriteLine(e.Message);
            }
            return null;
        }

然后在主函数中调用该方法

class Program
    {
        static void Main(string[] args)
        {
            XMLOperation xmlOpr = new XMLOperation();
            XmlNode xn=xmlOpr.getXmlNode("activity.xml", "2");
            string ActivityId = (xn.SelectSingleNode("ActivityId")).InnerText;
            string ActivityName = (xn.SelectSingleNode("ActivityName ")).InnerText;
            string ActivityLevel = xn.SelectSingleNode("ActivityLevel").InnerText;
            Console.WriteLine("ActivityId:" + ActivityId + "/nActivityName:" + ActivityName + "/nActivityLevel:" + ActivityLevel);
            Console.Read();
        }
    }

输出结果为：

ActivityId:2
ActivityName:pass
ActivityLevel:2