c#使用WebClient登录网站抓取登录后的网页

C#登录网站实际上就是模拟浏览器提交表单，然后记录浏览器响应返回的会话Cookie值，再次发送请求时带着这个会话cookie值去请求就可以实现模拟登录的效果了。

如下类CookieAwareWebClient实现在发送请求时都带着cookie。

public class CookieAwareWebClient : WebClient
{/* 何问起 hwq2.com */
    private CookieContainer cookie = new CookieContainer();

    protected override WebRequest GetWebRequest(Uri address)
    {
        WebRequest request = base.GetWebRequest(address);
        if (request is HttpWebRequest)
        {
            (request as HttpWebRequest).CookieContainer = cookie;
        }
        return request;
    }
}/* 何问起 hovertree.com */

如下是模拟表单提交登录的使用示例：

var client = new CookieAwareWebClient();
client.BaseAddress = @"https://hovertree.net/any/base/url/";
var loginData = new NameValueCollection();
loginData.Add("login", "YourLogin");
loginData.Add("password", "YourPassword");
client.UploadValues("login.php", "POST", loginData);

//Now you are logged in and can request pages
string htmlSource = client.DownloadString("index.php");/* 何问起 hwq2.com */

推荐：http://www.cnblogs.com/roucheng/p/csharpfetch.html