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QSerialPort::readyRead not responding



  • Hello,

    I am trying to implement Serial COM port program.
    The program is not responding to readyread event (I hope my understanding is not wrong).

    Here is the code:

    /* in .h */
    QSerialPort *serialData = nullptr;
    
    MainWindow::MainWindow(QWidget *parent) :
        QMainWindow(parent),
        ui(new Ui::MainWindow),
        serialData(new QSerialPort(this))
    {
        connect(ui->button_connect, &QPushButton::clicked, this, &MainWindow::openSerialPort);
        connect(serialData, &QSerialPort::errorOccurred, this, &MainWindow::handleCOMError);
        connect(serialData, &QSerialPort::readyRead, this, &MainWindow::readSerialData);
    }
    

    Open Serial port:

    void MainWindow::openSerialPort()
    {
        serialData = new QSerialPort();
        serialData->setPortName(ui->combo_commPort->currentText());
        serialData->setBaudRate(static_cast<QSerialPort::BaudRate>(baudRates[ui->combo_BaudRate->currentIndex()].baudRate));
        serialData->setDataBits(static_cast<QSerialPort::DataBits>(dataBits[ui->combo_DataBits->currentIndex()].dataBits));
        serialData->setParity(static_cast<QSerialPort::Parity>(parity[ui->combo_Parity->currentIndex()].Parity));
        serialData->setStopBits(static_cast<QSerialPort::StopBits>(stopBits[ui->combo_StopBits->currentIndex()].StopBits));
        serialData->setFlowControl(static_cast<QSerialPort::FlowControl>(flowControl[ui->combo_FlowControl->currentIndex()].FlowControl));
    
        if (serialData->open(QIODevice::ReadWrite)) {
            ui->button_connect->setDisabled(true);
            ui->tabWidget->setEnabled(true);
        } else {
            QMessageBox::critical(this, tr("Error"), serialData->errorString());
        }
    }
    

    This code is not triggered:

    void MainWindow::readSerialData()
    {
        const QByteArray data = serialData->readAll();
        ui->textEdit_recv->append(data);
    }
    

    To write data on COM :

    void MainWindow::on_button_send_clicked()
    {
        QByteArray str = ui->textEdit_send->toPlainText().toUtf8();
        serialData->write(str, str.length());
    }
    

    Please let me know a way to resolve this problem. Any pointers would be appreciated.

    -- CKP

    Note: I wrote most of this program by copying it from an example program - "Terminal Example"


  • Lifetime Qt Champion

    Where do you open the port?



  • I have updated the question with the code snippet that opens the COM port


  • Lifetime Qt Champion

    @PradeepCK You connect signals/slots before you create the QSerialPort instance?!
    This can't work...



  • Lo and behold - the code works now.

    Silly me,
    Thank you for pointing this out. You are a genius.

    -- CKP


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