服務端：

 class Program
    {
        private static MqttServer mqttServer = null;

        static void Main(string[] args)
        {
            MqttNetTrace.TraceMessagePublished += MqttNetTrace_TraceMessagePublished;
            new Thread(StartMqttServer).Start();

            while (true)
            {
                var inputString = Console.ReadLine().ToLower().Trim();

                if (inputString == "exit")
                {
                    mqttServer?.StopAsync();
                    Console.WriteLine("MQTT服務已停止！");
                    break;
                }
                else if (inputString == "clients")
                {
                    foreach (var item in mqttServer.GetConnectedClients())
                    {
                        Console.WriteLine($"客戶端標識：{item.ClientId}，協議版本：{item.ProtocolVersion}");
                    }
                }
                else
                {
                    Console.WriteLine($"命令[{inputString}]無效！");
                }
            }
        }

        private static void StartMqttServer()
        {
            if (mqttServer == null)
            {
                try
                {
                    var options = new MqttServerOptions
                    {
                        ConnectionValidator = p =>
                        {
                            if (p.ClientId == "c001")
                            {
                                if (p.Username != "u001" || p.Password != "p001")
                                {
                                    return MqttConnectReturnCode.ConnectionRefusedBadUsernameOrPassword;
                                }
                            }

                            return MqttConnectReturnCode.ConnectionAccepted;
                        }
                    };

                    mqttServer = new MqttServerFactory().CreateMqttServer(options) as MqttServer;
                    mqttServer.ApplicationMessageReceived += MqttServer_ApplicationMessageReceived;
                    mqttServer.ClientConnected += MqttServer_ClientConnected;
                    mqttServer.ClientDisconnected += MqttServer_ClientDisconnected;
                }
                catch (Exception ex)
                {
                    Console.WriteLine(ex.Message);
                    return;
                }
            }

            mqttServer.StartAsync();
            Console.WriteLine("MQTT服務啟動成功！");
        }

        private static void MqttServer_ClientConnected(object sender, MqttClientConnectedEventArgs e)
        {
            Console.WriteLine($"客戶端[{e.Client.ClientId}]已連線，協議版本：{e.Client.ProtocolVersion}");
        }

        private static void MqttServer_ClientDisconnected(object sender, MqttClientDisconnectedEventArgs e)
        {
            Console.WriteLine($"客戶端[{e.Client.ClientId}]已斷開連線！");
        }

        private static void MqttServer_ApplicationMessageReceived(object sender, MqttApplicationMessageReceivedEventArgs e)
        {
            Console.WriteLine($"客戶端[{e.ClientId}]>> 主題：{e.ApplicationMessage.Topic} 負荷：{Encoding.UTF8.GetString(e.ApplicationMessage.Payload)} Qos：{e.ApplicationMessage.QualityOfServiceLevel} 保留：{e.ApplicationMessage.Retain}");
        }

        private static void MqttNetTrace_TraceMessagePublished(object sender, MqttNetTraceMessagePublishedEventArgs e)
        {
            /*Console.WriteLine($">> 執行緒ID：{e.ThreadId} 來源：{e.Source} 跟蹤級別：{e.Level} 訊息: {e.Message}");

            if (e.Exception != null)
            {
                Console.WriteLine(e.Exception);
            }*/
        }
    }
 

客戶端

    class Program
    {
        private static MqttClient mqttClient = null;
        static string topic = "測試1/測試2/測試3";
        static void Main(string[] args)
        {

            mqttClient = new MqttClientFactory().CreateMqttClient() as MqttClient;
            mqttClient.ApplicationMessageReceived += MqttClient_ApplicationMessageReceived;
            mqttClient.Connected += MqttClient_Connected;
            mqttClient.Disconnected += MqttClient_Disconnected;

            var options = new MqttClientTcpOptions
            {
                Server = "127.0.0.1",
                ClientId = Guid.NewGuid().ToString().Substring(0, 5),
                UserName = "u001",
                Password = "p001",
                CleanSession = true
            };

            mqttClient.ConnectAsync(options);
            Console.ReadLine();
            Console.WriteLine("Hello World!");
        }
        private static void MqttClient_ApplicationMessageReceived(object sender, MqttApplicationMessageReceivedEventArgs e)
        {

            Console.WriteLine($">> {Encoding.UTF8.GetString(e.ApplicationMessage.Payload)}{Environment.NewLine}");

        }
        private static void MqttClient_Connected(object sender, EventArgs e)
        {

            Console.WriteLine("已連線到MQTT伺服器！" + Environment.NewLine);
            mqttClient.SubscribeAsync(new List<TopicFilter> {
                new TopicFilter(topic, MqttQualityOfServiceLevel.AtMostOnce)
            });
            Console.WriteLine($"已訂閱[{topic}]主題" + Environment.NewLine);
            //開始釋出訊息
            string inputString = "你好麼";
            var appMsg = new MqttApplicationMessage(topic, Encoding.UTF8.GetBytes(inputString), MqttQualityOfServiceLevel.AtMostOnce, false);
            mqttClient.PublishAsync(appMsg);
        }
        private static void MqttClient_Disconnected(object sender, EventArgs e)
        {

            Console.WriteLine("已斷開MQTT連線！" + Environment.NewLine);

        }
    }
 

原始碼下載地址：MQTT

MQTT Windows 端驗證程式： http://mqttfx.jensd.de/index.php/download