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一，引入qmqtt 库

我是将整个头文件/源文件都添加到了工程中进行编译，这样 跨平台时  方便，直接编译就行了。

原始仓库路径：https://github.com/emqx/qmqtt/tree/master

二，使用

声明一个单例类，将订阅到主题，直接以属性的方式 进行暴露，这样QML文件中 就可以直接使用。 下边是订阅一个温度 和湿度的主题数据。

#ifndef MQTTMANAGERT_H
#define MQTTMANAGERT_H#include <iostream>
#include <mqtt/qmqtt.h>class MQTTManager:public QObject
{Q_OBJECTQ_PROPERTY(QString inTemperature READ getInTemperature WRITE setInTemperature NOTIFY inTemperatureChanged FINAL)Q_PROPERTY(QString inHumidity READ getInHumidity WRITE setInHumidity NOTIFY inHumidityChanged FINAL)public:static MQTTManager* instance();QString getInTemperature() const;void setInTemperature(QString newInTemperature);QString getInHumidity() const;void setInHumidity(QString newInHumidity);private:~MQTTManager();MQTTManager();public slots:void doConnected();void onSubscribed(const QString& topic);void doDisconnected();void doDataReceived(QMQTT::Message message);signals:void inTemperatureChanged();void inHumidityChanged();private:QMQTT::Client *client;static MQTTManager *manager;QString inTemperature;QString inHumidity;
};
#endif // MQTTMANAGERT_H

#include "mqttManagert.h"MQTTManager* MQTTManager::manager=nullptr;const QString HOST= "127.0.0.1"; //服务器地址
//需要订阅的主题
const QString TOPIC_IN_TEMPERATURE_HUMIDITY ="qmqtt/in_temperature_humidity";MQTTManager::MQTTManager(){client = new QMQTT::Client(QHostAddress(HOST),1883,this);connect(client,&QMQTT::Client::connected,this,&MQTTManager::doConnected);connect(client,&QMQTT::Client::disconnected,this,&MQTTManager::doDisconnected);connect(client,&QMQTT::Client::received,this,&MQTTManager::doDataReceived);connect(client, &QMQTT::Client::subscribed, this, &MQTTManager::onSubscribed);client->connectToHost();
}MQTTManager::~MQTTManager(){client->disconnected();
}MQTTManager* MQTTManager::instance(){if(!manager){manager = new MQTTManager();}return manager;
}void MQTTManager::doConnected(){qDebug()<<"doConnected ok";//再此订阅主题client->subscribe(TOPIC_IN_TEMPERATURE_HUMIDITY);
}
void MQTTManager::onSubscribed(const QString& topic)
{qDebug() << "onSubscribed " << topic;
}void MQTTManager::doDataReceived(QMQTT::Message message){//收到消息QString mes = QString(message.id())+" "+QString(message.qos())+" "+message.topic()+" "+message.payload()+"\n";qDebug()<<"dataReceived "<<mes;//根据主题过滤消息if(message.topic()==TOPIC_IN_TEMPERATURE_HUMIDITY){QStringList dataList = QString(message.payload()).split(",");if(dataList.size()==2){setInTemperature(dataList[0]);setInHumidity(dataList[1]);}}}
void MQTTManager::doDisconnected(){qDebug()<<"doDisconnected ok";
}QString MQTTManager::getInTemperature() const
{return inTemperature;
}void MQTTManager::setInTemperature(QString newInTemperature)
{if (inTemperature == newInTemperature)return;inTemperature = newInTemperature;emit inTemperatureChanged();
}QString MQTTManager::getInHumidity() const
{return inHumidity;
}void MQTTManager::setInHumidity(QString newInHumidity)
{if (inHumidity == newInHumidity)return;inHumidity = newInHumidity;emit inHumidityChanged();
}