https://blog.csdn.net/dengyaan/article/details/51752327

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;
}
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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);

...
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作者：dengyaan
来源：CSDN
原文：https://blog.csdn.net/dengyaan/article/details/51752327
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