使用POST方式请求

string url = "http://localhost/BOOK/CH3/FirstServicecs.asmx/HelloWorld";
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
//POST方式请求
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
string strname= System.Web.HttpUtility.UrlEncode("name");
strname = strname + "=" + System.Web.HttpUtility.UrlEncode(textBox1.Text);
byte[] payload;//将URL编码后的字符串转化为字节
payload = System.Text.Encoding.UTF8.GetBytes(strname);
req.ContentLength = payload.Length;
Stream writer = req.GetRequestStream();
writer.Write(payload, 0, payload.Length); writer.Close();
HttpWebResponse response = (HttpWebResponse)req.GetResponse();
System.IO.Stream s;
s = response.GetResponseStream();
XmlTextReader reader =new XmlTextReader(s);
reader.MoveToContent();
label1.Text = reader.ReadInnerXml(); reader.Close();
using System;
using System.Web;
using System.Net;
using System.IO;
using System.Text;
namespace SendMessage
{

public bool SendMsg(MsgInfo msg)
{
//create request
try
{
WebRequest req = WebRequest.Create("http://your_post_url");

//set the request parameter
req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";

//querystring '?msg=xxx&type=0'
string strQuery = "msg=";
strQuery += HttpUtility.UrlEncode(msg);
strQuery += "&type=0";

string dataSend = strQuery;
req.ContentLength = dataSend.Length;

byte [] buff = Encoding.UTF8.GetBytes(dataSend);
Stream reqStream = req.GetRequestStream();
reqStream.Write(buff, 0, buff.Length);
reqStream.Close();

WebResponse rep = req.GetResponse();
Stream repStream = rep.GetResponseStream();
Encoding enc = Encoding.GetEncoding("utf-8");
StreamReader sr = new StreamReader(repStream, enc);

Char[] read = new Char[256];
sr.Read(read, 0, 256);

return true;
}
catch(NotSupportedException ns)
{
return false;
}
}

}

string url = "http://localhost:21240/ChangeHair/Receive.aspx?aa=5";//发送到的页面的地址
HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);

//读取一个图片
FileStream fs = new FileStream(Server.MapPath("~/NET基础知识.doc"), System.IO.FileMode.Open, System.IO.FileAccess.Read);
byte[] filecontent = new byte[fs.Length];
fs.Read(filecontent, 0, filecontent.Length);
fs.Close();
fs.Dispose();

//将图片转换成base64编码的流
string a = Convert.ToBase64String(filecontent);

//读取base64编码流，发送
byte[] requestBytes = System.Text.Encoding.Default.GetBytes(a);

req.Method = "POST";
req.ContentType = "application/x-www-form-urlencoded";
req.ContentLength = requestBytes.Length;
Stream requestStream = req.GetRequestStream();
requestStream.Write(requestBytes, 0, requestBytes.Length);
requestStream.Close();

//接收返回参数，到string backstr
HttpWebResponse res = (HttpWebResponse)req.GetResponse();
StreamReader sr = new StreamReader(res.GetResponseStream(), System.Text.Encoding.Default);
string backstr = sr.ReadToEnd();
sr.Close();
res.Close();
//输出参数
Response.Write(backstr);