1.添加Mqtt模块

      详情根据这篇文章  https://blog.csdn.net/m0_56942491/article/details/132516553

2.根据官方的例程原地修改

找到官方例程，在QT中打开简易客户端的工程。

在ui设计中在原基础上添加三个lineEdit文本框。分别在原名基础上添加Username,Clientid,Password。
 

// Copyright (C) 2017 The Qt Company Ltd.
// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause

#include "mainwindow.h"
#include "ui_mainwindow.h"

#include <QtCore/QDateTime>
#include <QtMqtt/QMqttClient>
#include <QtWidgets/QMessageBox>

using namespace Qt::StringLiterals;

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    m_client = new QMqttClient(this);
    m_client->setHostname(ui->lineEditHost->text());
    m_client->setClientId(ui->lineEditClientid->text());
    m_client->setUsername(ui->lineEditUsername->text());
    m_client->setPassword(ui->lineEditPassword->text());
    m_client->setKeepAlive(1000);
    m_client->setProtocolVersion(QMqttClient::MQTT_3_1);
    m_client->setPort(static_cast<quint16>(ui->spinBoxPort->value()));

    connect(m_client, &QMqttClient::stateChanged, this, &MainWindow::updateLogStateChange);
    connect(m_client, &QMqttClient::disconnected, this, &MainWindow::brokerDisconnected);

    connect(m_client, &QMqttClient::messageReceived, this, [this](const QByteArray &message, const QMqttTopicName &topic) {
        const QString content = QDateTime::currentDateTime().toString()
                    + " Received Topic: "_L1
                    + topic.name()
                    + " Message: "_L1
                    + message
                    + u'\n';
        ui->editLog->insertPlainText(content);
    });

    connect(m_client, &QMqttClient::pingResponseReceived, this, [this]() {
        const QString content = QDateTime::currentDateTime().toString()
                    + "PingResponse\n"_L1;
        ui->editLog->insertPlainText(content);
    });

    connect(ui->lineEditHost, &QLineEdit::textChanged, m_client, &QMqttClient::setHostname);
    connect(ui->lineEditClientid, &QLineEdit::textChanged, m_client, &QMqttClient::setClientId);
    connect(ui->lineEditUsername, &QLineEdit::textChanged, m_client, &QMqttClient::setUsername);
    connect(ui->lineEditPassword, &QLineEdit::textChanged, m_client, &QMqttClient::setPassword);
    connect(ui->spinBoxPort, QOverload<int>::of(&QSpinBox::valueChanged), this, &MainWindow::setClientPort);
    updateLogStateChange();
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_buttonConnect_clicked()
{
    if (m_client->state() == QMqttClient::Disconnected) {
        ui->lineEditHost->setEnabled(false);
        ui->spinBoxPort->setEnabled(false);
        ui->buttonConnect->setText(tr("Disconnect"));
        m_client->connectToHost();
    } else {
        ui->lineEditHost->setEnabled(true);
        ui->spinBoxPort->setEnabled(true);
        ui->buttonConnect->setText(tr("Connect"));
        m_client->disconnectFromHost();
    }
}

void MainWindow::on_buttonQuit_clicked()
{
    QApplication::quit();
}

void MainWindow::updateLogStateChange()
{
    const QString content = QDateTime::currentDateTime().toString()
                    + ": State Change"_L1
                    + QString::number(m_client->state())
                    + u'\n';
    ui->editLog->insertPlainText(content);
}

void MainWindow::brokerDisconnected()
{
    ui->lineEditHost->setEnabled(true);
    ui->spinBoxPort->setEnabled(true);
    ui->buttonConnect->setText(tr("Connect"));
}

void MainWindow::setClientPort(int p)
{
    m_client->setPort(static_cast<quint16>(p));
}

void MainWindow::on_buttonPublish_clicked()
{
    if (m_client->publish(ui->lineEditTopic->text(), ui->lineEditMessage->text().toUtf8()) == -1)
        QMessageBox::critical(this, u"Error"_s, u"Could not publish message"_s);
}

void MainWindow::on_buttonSubscribe_clicked()
{
    auto subscription = m_client->subscribe(ui->lineEditTopic->text());
    if (!subscription) {
        QMessageBox::critical(this, u"Error"_s,
                              u"Could not subscribe. Is there a valid connection?"_s);
        return;
    }
}

让后在mainwindow.c文件中添加ui设计中像例程中的Hostname一样添加信号与槽函数就行了。

3.设置参数

根据自己的华为云中的连接参数添加

参数填完后点击connect就可以了

可以看到已经连接上了。