用C#遍历XML

using System;
using System.Drawing;
using System.Collections;
using System.ComponentModel;
using System.Windows.Forms;
using System.Data;
using System.Xml;
namespace WindowsApplication3
{
    ///
    /// Form1 的摘要说明。
    ///
    public class Form1 : System.Windows.Forms.Form
    {
        private System.Windows.Forms.Button button1;
        private XmlDocument doc = new XmlDocument();
        private     XmlNode attrColl;
        private System.Windows.Forms.Button button2;
        private System.Windows.Forms.HelpProvider helpProvider1;
        ///
        /// 必需的设计器变量。
        ///
        private System.ComponentModel.Container components = null;
        public Form1()
        {
       //
       // Windows 窗体设计器支持所必需的
       //