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前言

基于QT5.15版本，使用QtMqtt链接。

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提示：以下是本篇文章正文内容，下面案例可供参考

QtMqtt编译

从QtMqtt[源码地址](https://github.com/qt/qtmqtt)克隆项目到本地。在Qt编译环境的include文件夹（根据配置的compiler会有不同的路径，windows默认路径是C:\Qt\Qt-5.15.2\include）内建立QtMqtt文件夹，将/src/mqtt目录下的头文件复制刚刚新建的QtMqtt文件夹内。编译目标环境的Release版本，生成链接库（windows是.dll文件和.lib文件）。将生成的链接库复制到编译环境的lib文件夹，windows环境还需要将.dll文件复制bin文件夹。

注意：本人的目标机环境是Linux，以下代码均基于此实现

代码实现

1.引入库

在qpro文件内添加一行

LIBS     += -lQt5Mqtt

2.头文件

代码如下（示例）：

#ifndef MQTTCONSUMER_H
#define MQTTCONSUMER_H
#include <QtMqtt/qmqttclient.h>
#include <QTimer>
#include <QObject>class Mqtt : public QObject
{Q_OBJECT
public:explicit Mqtt(QObject *parent = nullptr);//设置最大延迟链接时间void setReconnectMaxDelayTime(int i){m_maxDelay = i;}//发送消息void publishMessage(const QString &message, const QString &topic);//增加订阅void addTopic(const QString &topic);//移除订阅void removeTopic(const QString &topic);public slots:void subscribe();private:QMqttClient* _client = new QMqttClient() ;QTimer *_timer = new QTimer(this);//最大延迟连接时间int m_maxDelay = 900000;int m_time = 1000;QStringList m_topics;
};#endif // MQTTCONSUMER_H

3.cpp文件

#include "mqtt.h"Mqtt::Mqtt(QObject *parent) : QObject(parent)
{_client->setHostname("127.0.0.1");_client->setPort(1883);_client->connectToHost();//链接断开时进行重连connect(_client, &QMqttClient::disconnected, this, [this](){_timer->start(m_time);});//链接成功时进行订阅connect(_client, &QMqttClient::connected, this, [this](){subscribe();});//有消息时进行消费connect(_client, &QMqttClient::messageReceived, this, [](const QByteArray &message, const QMqttTopicName &topic) {const QString content = QDateTime::currentDateTime().toString()+ QLatin1String(" Received Topic: ")+ topic.name()+ QLatin1String(" Message: ")+ message+ QLatin1Char('\n');qDebug() << content;});//触发重新计时器connect(_timer, &QTimer::timeout, this, [this](){//重新链接_client->connectToHost();//如果延迟时间小于最大延迟时间则加15秒if(m_time < m_maxDelay){m_time = m_time + 15000;}        qDebug() << QString("reconnect times: %1").arg((m_time - 1000) / 15000);//一定要停止当前的计时器_timer->stop();});
}void Mqtt::publishMessage(const QString &message, const QString &topic)
{if(_client->state() == QMqttClient::Connected){qint32 localPublish = _client->publish(topic, message.toUtf8());if(localPublish < 0){qDebug() << QString("send message : %1 to topic: %2 faild.").arg(message).arg(topic);}}
}void Mqtt::addTopic(const QString &topic)
{if(!m_topics.contains(topic)){m_topics << topic;QMqttSubscription *localSubscribe = _client->subscribe(topic);if(!localSubscribe){qDebug() << QString("subscribe topic : %1 faild.").arg(topic);}else{qDebug() << QString("subscribe topic : %1 succes.").arg(topic);}}
}void Mqtt::removeTopic(const QString &topic)
{_client->unsubscribe(topic);m_topics.removeOne(topic);
}void Mqtt::subscribe()
{//链接成功后停止计时器，重置重连延迟时间，订阅主题_timer->stop();m_time = 1000;for(QString topic : m_topics){QMqttSubscription *localSubscribe = _client->subscribe(topic);if(!localSubscribe){qDebug() << QString("subscribe topic : %1 faild.").arg(topic);}else{qDebug() << QString("subscribe topic : %1 succes.").arg(topic);}}
}

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总结

由于目标机和开发机不是同一环境，涉及到交叉编译的情况，编译环境一定要搞清楚！！！