string regid =“fcm_reg_id1,fcm_reg_id2”就像这样.

string applicationID =“abcd”;

string SENDER_ID =“123456”;

string regid="c_Z5yRoj4TY:APA91bGry2g_CIA1xaRy_LscxOvFX6YHqasKA96TjpG6yi1yytNyM5rtGL6DgxjGMSE5c74d7VdSL6W8zxO1ixVMlpVMwdgcrsGUWV0VfdbddC2XD","c_Z5yRoj4TY:APA91bGry2g_CIA1xaRy_LscxOvFX6YHqasKA96TjpG6yi1yytNyM5rtGL6DgxjGMSE5c74d7";

            HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create("https://fcm.googleapis.com/fcm/send");

            httpWebRequest.ContentType = "application/x-www-form-urlencoded;charset=UTF-8";

            httpWebRequest.Method = "POST";

            String collaps_key = "score_update";

            string json = "collapse_key=abcd" + "&data.header=cricket&registration_id=" + regId + "&data.notificationId=" + notificationId + "&data.message=" + msg;

            httpWebRequest.Headers.Add(string.Format("Authorization: key={0}",applicationID));
            httpWebRequest.Headers.Add(string.Format("Sender: key={0}",SENDER_ID));

            using (var streamWriter = new StreamWriter(httpWebRequest.GetRequestStream()))
            {
                //Console.WriteLine(json);
                streamWriter.Write(json);
                streamWriter.Flush();
                streamWriter.Close();
                using (HttpWebResponse httpResponse = (HttpWebResponse)httpWebRequest.GetResponse())
                {
                    using (var streamReader = new StreamReader(httpResponse.GetResponseStream()))
                    {
                        var result = streamReader.ReadToEnd();
                        Console.WriteLine(result);
                        retmsgid = result.ToString();
                        if (retmsgid.Trim() != "")
                        {
                            ResponceString = result.ToString();
                            string[] msgsplits = retmsgid.Split(',');
                            string[] msg1 = msgsplits[0].ToString().Split(':');
                            ReturnMessageId = msg1[1].ToString();
                        }
                        else
                        {
                            ReturnMessageId = "0";
                        }
                    }
                    httpResponse.Close();
                    httpResponse.Dispose();
                    httpWebRequest = null;
                }
            }