c#（winform）抓取网页源码和链接

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Net;
using System.IO;

namespace pachong
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            HttpWebRequest request;   //HttpWebRequest和HttpWebResponse类是用于发送和接收HTTP数据


            HttpWebResponse response;   //这两个类位 于System.Net命名空间，默认情况下这个类对于控制台程序来说是可访问的。

            TextReader tr;    //Text的读取器

            string url = textBox1.Text.ToString();
            request = (HttpWebRequest)WebRequest.Create(url);  //为指定的url方案初始化新的实例

            response = (HttpWebResponse)request.GetResponse();  //返回来自internet资源的响应

            tr = new StreamReader(response.GetResponseStream(), Encoding.GetEncoding(936));

            textBox2.Text = tr.ReadToEnd();
            response.Close();
            WebExpress(textBox2.Text.ToString());
        }
        private void WebExpress(string s)
        {
            string tag1 = "<a href=";
            string tag2 = ">";
            /*IndexOf()方法搜索在该字符串上是否出现了作为参数传递的字符串,
             * 如果找到字符串,则返回字符的起始位置 
             * (0表示第一个字符,1表示第二个字符依此类推)如果说没有找到则返回 -1*/

            int pos3, pos2, pos1 = s.IndexOf(tag1);  //指定字符串在实例中的第一个匹配串的索引

            while (pos1 > 0)
            {
                pos2 = s.IndexOf(tag2, pos1 + 1);
                if (pos2 < 0)
                    return;
                pos3 = s.IndexOf(" ", pos1 + 5);
                if (pos3 > 0 && pos3 < pos2)
                    pos2 = pos3;
                string url = s.Substring(pos1 + tag1.Length, pos2 - pos1 - tag1.Length);
                url = url.Replace("\"", "");
                if (url.IndexOf("http") >= 0)
                    textBox3.Text += url + "\n";
                else url = url + "http://nbubs.nbu.edu.cn";
                textBox3.Text += url + "\n";
                s = s.Substring(pos2 + 1);
                pos1 = s.IndexOf(tag1);
            }
        }
    }
}