使用WebClient发送POST请求

   ///   <summary>
     ///  发送post请求
     ///   </summary>
     ///   <param name="url"> 请求的url </param>
     ///   <param name="postString"> 发送到数据 例如:"name=xhan&password=1231" </param>
     ///   <param name="encoding"> 发送和接受数据使用的编码 </param>
     ///   <returns> 服务器响应字符串 </returns>
     public   static   string  SendPostRequest( string  url,  string  postString,Encoding encoding)
    {
         byte [] postData  =  encoding.GetBytes(postString);

        WebClient client  =   new  WebClient();
        client.Headers.Add( " Content-Type " ,  " application/x-www-form-urlencoded " );
        client.Headers.Add( " ContentLength " , postData.Length.ToString());

         byte [] responseData  =  client.UploadData(url,  " POST " , postData);
         return  encoding.GetString(responseData);
    }