MQTT 客户端应用及常见问题（C#）

最近因为工作需要，需要使用C# 语言编写一个通过MQTT协议 ，上传数据到云端的工具。因为之前没有用过MQTT，所以 使用的时候遇到很多问题.下面将会把我遇到的问题一一解释。

1.引用源码库地址
https://github.com/eclipse/paho.mqtt.m2mqtt
2.说明
https://m2mqtt.wordpress.com/m2mqtt_doc/
3.使用后遇到的问题
当网络中断后,MQTT 程序有时候不会自动重连。
解决方案 添加监控MQTT连接状态

1.添加全局静态变量 uPLibrary.Networking.M2Mqtt.MQTTConfig.IsSocketRun;

class MQTTConfig{ public static bool IsSocketRun = false;}

2.修改MqttClient 类 的Connect 方法，在连接成功后把IsSocketRun = true.
MQTTConfig.IsSocketRun = true;

  /// <summary>        /// Connect to broker        /// </summary>        /// <param name="clientId">Client identifier</param>        /// <param name="username">Username</param>        /// <param name="password">Password</param>        /// <param name="willRetain">Will retain flag</param>        /// <param name="willQosLevel">Will QOS level</param>        /// <param name="willFlag">Will flag</param>        /// <param name="willTopic">Will topic</param>        /// <param name="willMessage">Will message</param>        /// <param name="cleanSession">Clean sessione flag</param>        /// <param name="keepAlivePeriod">Keep alive period</param>        /// <returns>Return code of CONNACK message from broker</returns>        public byte Connect(string clientId,            string username,            string password,            bool willRetain,            byte willQosLevel,            bool willFlag,            string willTopic,            string willMessage,            bool cleanSession,            ushort keepAlivePeriod)        {            // create CONNECT message            MqttMsgConnect connect = new MqttMsgConnect(clientId,                username,                password,                willRetain,                willQosLevel,                willFlag,                willTopic,                willMessage,                cleanSession,                keepAlivePeriod,                (byte)this.ProtocolVersion);            try            {                // connect to the broker                this.channel.Connect();            }            catch (Exception ex)            {                throw new MqttConnectionException("Exception connecting to the broker", ex);            }            this.lastCommTime = 0;            this.isRunning = true;            MQTTConfig.IsSocketRun = true;            this.isConnectionClosing = false;            // start thread for receiving messages from broker            Fx.StartThread(this.ReceiveThread);....

3.继续修改 MqttClient .cs类中的Ping() 方法

/// <summary>/// Execute ping to broker for keep alive/// </summary>/// <returns>PINGRESP message from broker</returns>private MqttMsgPingResp Ping(){    MqttMsgPingReq pingreq = new MqttMsgPingReq();    try    {        // broker must send PINGRESP within timeout equal to keep alive period        return (MqttMsgPingResp)this.SendReceive(pingreq, this.keepAlivePeriod);    }    catch (Exception e)    {#if TRACE        MqttUtility.Trace.WriteLine(TraceLevel.Error, "Exception occurred: {0}", e.ToString());#endif        MQTTConfig.IsSocketRun = false;        // client must close connection        this.OnConnectionClosing();        return null;    }}

4.最后在我们程序集入口初始化程序的时候 添加线程调用 。当MQTT中断后就会自动重连 ，另外提醒方法异常时一定要异常处理哦。

while (true)            {                    LogWriter.DebugLog(string.Format("执行次数{0}  IsSocketRun {1}", i, uPLibrary.Networking.M2Mqtt.MQTTConfig.IsSocketRun));                    if (!uPLibrary.Networking.M2Mqtt.MQTTConfig.IsSocketRun)                   {        程序执行到吗。。。    }        System.Threading.Thread.Sleep(10000);}

MQTT 订阅

// create client instance MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS)); // register to message received client.MqttMsgPublishReceived += client_MqttMsgPublishReceived; string clientId = Guid.NewGuid().ToString(); client.Connect(clientId); // subscribe to the topic "/home/temperature" with QoS 2 client.Subscribe(new string[] { "/home/temperature" }, new byte[] { MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE }); ... static void client_MqttMsgPublishReceived(object sender, MqttMsgPublishEventArgs e) { // handle message received } 

MQTT 发布

…

// create client instance MqttClient client = new MqttClient(IPAddress.Parse(MQTT_BROKER_ADDRESS)); string clientId = Guid.NewGuid().ToString(); client.Connect(clientId); string strValue = Convert.ToString(value); // publish a message on "/home/temperature" topic with QoS 2 client.Publish("/home/temperature", Encoding.UTF8.GetBytes(strValue), MqttMsgBase.QOS_LEVEL_EXACTLY_ONCE, false); ...