网页自动登录（提交Post内容）的用途很多，如验证身份、程序升级、网络投票等，以下是用C#实现的方法。
网页自动登录和提交POST信息的核心就是分析网页的源代码（HTML），在C#中，可以用来提取网页HTML的组件比较多，常用的用WebBrowser、WebClient、HttpWebRequest这三个。以下就分别用这三种方法来实现：
1、WebBrowser是个"迷你"浏览器，其特点是Post时不用关心Cookie、内置JS等问题
WebBrowser是VS2005新提供的组件（其实就是封装了IE接口），实现POST功能一般在webBrowser的DocumentCompleted中分析HtmlDocument 来实现，代码如下：

HtmlElement ClickBtn =null;
if (e.Url.ToString().ToLower().IndexOf("xxx.htm") > 0) //登陆页面
{
HtmlDocument doc = webBrowser1.Document;
for (int i = 0; i < doc.All.Count ; i++)
{
if (doc.All[i].TagName.ToUpper().Equals("INPUT"))
{
switch (doc.All[i].Name)
{
case "userCtl":
doc.All[i].InnerText = "user01";
break;
case "passCt1":
doc.All[i].InnerText = "mypass";
break;
case "B1":
ClickBtn = doc.All[i]; //提交按钮
break;
}
}
}
ClickBtn.InvokeMember("Click"); //执行按扭操作
}
2、WebClient封装了HTTP的一些类，操作简单，相较于webBrowser，特点是可以自设代理，缺点是对COOKIE的控制
WebClient的运行全在后台，并且提供了异步操作的能力，这样很方便并发多个任务，然后等待结果的返回，再逐个处理。多任务异步调用的代码如下：

private void StartLoop(int ProxyNum)
{
WebClient [] wcArray = new WebClient[ProxyNum]; //初始化
for (int idArray = 0; idArray< ProxyNum;idArray++)
{
wcArray[idArray] = new WebClient();
wcArray[idArray].OpenReadCompleted += new OpenReadCompletedEventHandler(Pic_OpenReadCompleted2);
wcArray[idArray].UploadDataCompleted += new UploadDataCompletedEventHandler(Pic_UploadDataCompleted2);
try
{
......
wcArray[idArray].Proxy = new WebProxy(proxy[1], port);
wcArray[idArray].OpenReadAsync(new Uri("http://xxxx.com.cn/tp.aspId=129")); //打开WEB;
proxy = null;
}
catch
{
}
}
}

private void Pic_OpenReadCompleted2(object sender, OpenReadCompletedEventArgs e)
{
if (e.Error == null)
{
string textData = new StreamReader(e.Result, Encoding.Default).ReadToEnd(); //取返回信息
.....
String cookie = ((WebClient)sender).ResponseHeaders["Set-Cookie"];
((WebClient)sender).Headers.Add("Content-Type", "application/x-www-form-urlencoded");
((WebClient)sender).Headers.Add("Accept-Language", "zh-cn");
((WebClient)sender).Headers.Add("Cookie", cookie);

string postData = "......"
byte[] byteArray = Encoding.UTF8.GetBytes(postData); // 转化成二进制数组
((WebClient)sender).UploadDataAsync(new Uri("http://xxxxxxy.com.cn/tp.aspId=129"), "POST", byteArray);
}
}

private void Pic_UploadDataCompleted2(object sender, UploadDataCompletedEventArgs e)
{
if (e.Error == null)
{
string returnMessage = Encoding.Default.GetString(e.Result);
......
}
}


3、HttpWebRequest较为低层，能实现的功能较多，Cookie操作也很简单 

private bool PostWebRequest()
{
CookieContainer cc = new CookieContainer();
string pos tData = "user=" + strUser + "&pass=" + strPsd;
byte[] byteArray = Encoding.UTF8.GetBytes(postData); // 转化

HttpWebRequest webRequest2 = (HttpWebRequest)WebRequest.Create(new Uri("http://www.xxxx.com/chk.asp"));
webRequest2.CookieContainer = cc;
webRequest2.Method = "POST";
webRequest2.ContentType = "application/x-www-form-urlencoded";
webRequest2.ContentLength = byteArray.Length;
Stream newStream = webRequest2.GetRequestStream();
//Sendthedata.
newStream.Write(byteArray, 0, byteArray.Length); //写入参数
newStream.Close();

HttpWebResponse response2 = (HttpWebResponse)webRequest2.GetResponse();
StreamReader sr2=new StreamReader(response2.GetResponseStream(), Encoding.Default);
string text2 = sr2.ReadToEnd();
......
}
HttpWebRequest同样提供了异步操作，有兴趣的朋友自己查MSDN