Simple MQTT Client Example

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#include "mainwindow.h" #include "ui_mainwindow.h" #include <QtCore/QDateTime> #include <QtMqtt/QMqttClient> #include <QtWidgets/QMessageBox> 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->setPort(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() + QLatin1String(" Received Topic: ") + + QLatin1String(" Message: ") + message + QLatin1Char('\n'); ui->editLog->insertPlainText(content); }); connect(m_client, &QMqttClient::pingResponseReceived, this, [this]() { const QString content = QDateTime::currentDateTime().toString() + QLatin1String(" PingResponse") + QLatin1Char('\n'); ui->editLog->insertPlainText(content); }); connect(ui->lineEditHost, &QLineEdit::textChanged, m_client, &QMqttClient::setHostname); 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() + QLatin1String(": State Change") + QString::number(m_client->state()) + QLatin1Char('\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(p); } void MainWindow::on_buttonPublish_clicked() { if (m_client->publish(ui->lineEditTopic->text(), ui->lineEditMessage->text().toUtf8()) == -1) QMessageBox::critical(this, QLatin1String("Error"), QLatin1String("Could not publish message")); } void MainWindow::on_buttonSubscribe_clicked() { auto subscription = m_client->subscribe(ui->lineEditTopic->text()); if (!subscription) { QMessageBox::critical(this, QLatin1String("Error"), QLatin1String("Could not subscribe. Is there a valid connection?")); return; } }