在nuGet下载M2Mqtt   V4.3.0版本。（支持.net framework）

订阅主题

public void LoadMQQCData()
{
    string enpoint = "xxx.xxx.x.x";//ip地址
    int port = 1883;//端口
    string user = "usrname";//用户名
    string pwd = "pwd";//密码
    string clientid = Guid.NewGuid().ToString(); // 获取一个独一无二的id
    string[] topic = new string[] { "topic" };//订阅主题

    byte[] qosLevels = new byte[] { MqttMsgBase.QOS_LEVEL_AT_LEAST_ONCE }; // qos=1

    MqttClient client = new MqttClient(enpoint, port, false, null, null, MqttSslProtocols.None);
    //消息接受
    client.MqttMsgPublishReceived += new MqttClient.MqttMsgPublishEventHandler(messageReceive);
    //连接Broker
    client.Connect(clientid, user, pwd);
    client.Subscribe(topic, qosLevels);

}

接收数据

static void messageReceive(object sender, MqttMsgPublishEventArgs e)
{
    Thread.Sleep(1000 * 30);//等待半分钟 等待质控数据入库
    //接收到的数据
    byte[] Bytes = e.Message;
    //获取站点编号
    try
    {
        string sstation = e.Topic.Substring(e.Topic.IndexOf("qc") - 10, 9);
        if (!string.IsNullOrEmpty(sstation) && sstation.Length == 9)
        { //代表该（SS4201089）站点做了质控
            do some things;
        }
    }
    catch (Exception ex)
    {
        MessageServcie.Instance.OnShowMessageDelegate.Invoke("出错：" + ex.Message.ToString(), false);
    }

}