C# 如何在Windows phone中将字符串发送到url？

我在类中创建了一个方法（不在手机应用程序中）：

但它会出现这样的错误： “System.Net.HttpWebRequest”不包含“GetRequestStream”的定义，并且找不到接受“System.Net.HttpWebRequest”类型的第一个参数的扩展方法“GetRequestStream”（是否缺少using指令或程序集引用？ 我不知道为什么？请帮帮我

//Create web request for Post Method
public  void testSend()
  {
      try
      {
          string url = "abc.com";
          string str = "test";
          HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
          req.Method = "POST";
          req.ContentType = "application/x-www-form-urlencoded";
          req.BeginGetRequestStream(SendRequest, req);
      }
      catch (WebException)
      {

      }
}

//Get Response and write body
 private void SendRequest(IAsyncResult asyncResult)
        {
          string str = "test";
          string Data = "data=" + str;
          HttpWebRequest req= (HttpWebRequest)asyncResult.AsyncState;
          byte[] postBytes = Encoding.UTF8.GetBytes(Data);
          req.ContentType = "application/x-www-form-urlencoded";
          req.ContentLength = postBytes.Length;
          Stream requestStream = req.GetRequestStream();
          requestStream.Write(postBytes, 0, postBytes.Length);
          requestStream.Close();
          request.BeginGetResponse(SendResponse, req);
        }

//Get Response string
 private void SendResponse(IAsyncResult asyncResult)
        {
            try
            {
                MemoryStream ms;

                HttpWebRequest request = (HttpWebRequest)asyncResult.AsyncState;
                HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asyncResult);
                HttpWebResponse httpResponse = (HttpWebResponse)response;
                string _responestring = string.Empty;
                using (Stream data = response.GetResponseStream())
                using (var reader = new StreamReader(data))
                {
                    _responestring = reader.ReadToEnd();
                 }
              }
       catch (WebException)
      {

      }
   }

//Create web request for Post Method
public  void testSend()
  {
      try
      {
          string url = "abc.com";
          string str = "test";
          HttpWebRequest req = (HttpWebRequest)WebRequest.Create(url);
          req.Method = "POST";
          req.ContentType = "application/x-www-form-urlencoded";
          req.BeginGetRequestStream(SendRequest, req);
      }
      catch (WebException)
      {

      }
}

//Get Response and write body
 private void SendRequest(IAsyncResult asyncResult)
        {
          string str = "test";
          string Data = "data=" + str;
          HttpWebRequest req= (HttpWebRequest)asyncResult.AsyncState;
          byte[] postBytes = Encoding.UTF8.GetBytes(Data);
          req.ContentType = "application/x-www-form-urlencoded";
          req.ContentLength = postBytes.Length;
          Stream requestStream = req.GetRequestStream();
          requestStream.Write(postBytes, 0, postBytes.Length);
          requestStream.Close();
          request.BeginGetResponse(SendResponse, req);
        }

//Get Response string
 private void SendResponse(IAsyncResult asyncResult)
        {
            try
            {
                MemoryStream ms;

                HttpWebRequest request = (HttpWebRequest)asyncResult.AsyncState;
                HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asyncResult);
                HttpWebResponse httpResponse = (HttpWebResponse)response;
                string _responestring = string.Empty;
                using (Stream data = response.GetResponseStream())
                using (var reader = new StreamReader(data))
                {
                    _responestring = reader.ReadToEnd();
                 }
              }
       catch (WebException)
      {

      }
   }