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;

  /// 

        /// Connect to broker
        /// 
        /// Client identifier
        /// Username
        /// Password
        /// Will retain flag
        /// Will QOS level
        /// Will flag
        /// Will topic
        /// Will message
        /// Clean sessione flag
        /// Keep alive period
        /// Return code of CONNACK message from broker
        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

/// 

/// Execute ping to broker for keep alive
/// 
/// PINGRESP message from broker
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); 

...