之前研究各种语言异步的时候就想做一个C#版本的异步，但是毕竟好久不做了（也就是在大学期间用asp.net做了几个管理系统）
一开始写代码时完全蒙蔽了，语法啥的都忘差不多了~~研究了好几天，也参考了网上许多资料，终于写出了几行low逼代码
实现内容：异步并发爬取网页信息
首先异步的语法和其他语言都大同小异，async、await，定义异步方法的话要加async修饰符，如果你想在await调用，那么返回值必须为 Task
若返回值为Task，但是我们并没有await，也就是阻塞时返回继续执行，VS编译器也会给予提示，但可以正常运行
接下来说一下爬取程序的实现，也是也很简单，就是HTML匹配抓取关键字
先写一个方法 实现文本截取
public static string get_key_by_content(string content, string start, string end){if (content.Contains(start) && content.Contains(end)){int start_point = content.IndexOf(start, 0, System.StringComparison.Ordinal) + start.Length;int end_point = content.IndexOf(end, start_point, System.StringComparison.Ordinal);return content.Substring(start_point, end_point - start_point);}else{return "";}}以CSDN博客为例，截取标题、阅读量等信息
我们发现标题有一个超链接，于是我们把帖子的子url摘出来
string link_view = Common.get_key_by_content(content, "<span class=\"link_view\" title=\"阅读次数\">", "</span>");string link_title = Common.get_key_by_content(content, "<span class=\"link_title\"><a href=\"/"+childurl+"\">", "</a>");
整个爬取函数：
static async Task Spider(string RootUrl, int child, string childurl){using (var client = new HttpClient()){client.BaseAddress = new Uri(RootUrl);client.DefaultRequestHeaders.Accept.Clear();client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("text/html"));try{HttpResponseMessage response = await client.GetAsync(childurl);response.EnsureSuccessStatusCode();string content = await response.Content.ReadAsStringAsync();string link_view = Common.get_key_by_content(content, "<span class=\"link_view\" title=\"阅读次数\">", "</span>");string link_title = Common.get_key_by_content(content, "<span class=\"link_title\"><a href=\"/"+childurl+"\">", "</a>");Console.WriteLine("第" + (child + 1).ToString() + "个帖子 " + link_title+" "+link_view);}catch (HttpRequestException e){Console.WriteLine(e.Message);}}}然后我们定义执行异步任务函数
static async void StartTask(string url){for (int p = 0; p < Common.get_article_length(); p++){//await WhileRun(url, p, Common.get_article_by_id(p));WhileRun(url, p, Common.get_article_by_id(p));}}static async Task WhileRun(string RootUrl, int p, string childurl){while (true){await Spider(RootUrl, p, childurl);Thread.Sleep(1000);}}接下来只要定义几个帖子就可以了，由于C#没有全局的概念，所以我们要封装成一个类，同时给出获取帖子地址、帖子总数长度等方法。
完整代码：
using System;using System.Collections.Generic;using System.IO;using System.Net.Http;using System.Net.Http.Headers;using System.Text;using System.Threading;using System.Threading.Tasks;public class Common{static string[] articles = {"sm9sun/article/details/75395020","sm9sun/article/details/75446875","sm9sun/article/details/75449050","sm9sun/article/details/75735001","sm9sun/article/details/75309443","sm9sun/article/details/76358660"};public static string get_article_by_id(int id){if(id < articles.Length&&id>=0){return articles[id];}else{return "error";}}public static int get_article_length(){return articles.Length;}public static string get_key_by_content(string content, string start, string end){if (content.Contains(start) && content.Contains(end)){int start_point = content.IndexOf(start, 0, System.StringComparison.Ordinal) + start.Length;int end_point = content.IndexOf(end, start_point, System.StringComparison.Ordinal);return content.Substring(start_point, end_point - start_point);}else{return "";}}}class Program{static void Main(){string RootUrl = "http://blog.csdn.net";StartTask(RootUrl);Console.WriteLine("gogogo!");Console.ReadLine();}static async void StartTask(string url){for (int p = 0; p < Common.get_article_length(); p++){//await WhileRun(url, p, Common.get_article_by_id(p));WhileRun(url, p, Common.get_article_by_id(p));}}static async Task WhileRun(string RootUrl, int p, string childurl){while (true){await Spider(RootUrl, p, childurl);Thread.Sleep(1000);}}static async Task Spider(string RootUrl, int child, string childurl){using (var client = new HttpClient()){client.BaseAddress = new Uri(RootUrl);client.DefaultRequestHeaders.Accept.Clear();client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("text/html"));try{HttpResponseMessage response = await client.GetAsync(childurl);response.EnsureSuccessStatusCode();string content = await response.Content.ReadAsStringAsync();string link_view = Common.get_key_by_content(content, "<span class=\"link_view\" title=\"阅读次数\">", "</span>");string link_title = Common.get_key_by_content(content, "<span class=\"link_title\"><a href=\"/"+childurl+"\">", "</a>");Console.WriteLine("第" + (child + 1).ToString() + "个帖子 " + link_title+" "+link_view);}catch (HttpRequestException e){Console.WriteLine(e.Message);}}}}运行截图：
顺带一提，我不是故意刷阅读量的~！~！
不是~！~！
真的不是~！~！
随时随地看视频
