Problem with QSerialPort::readyRead signal

Stefanoxjx

Hi at all,
I've a problem with QSerialPort and readyRead signal.
Seems that this signal is called one time, only when connect signal/slot function is executed.
I placed a breakpoint in this slot but when I receive data from serial port this slot is not called.
I've seen that this problem was in Qt 5.12.5~5.13.0 but I use 5.15.2 and I haven't seen any reports about this version.
This is my code:

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>
#include <QtSerialPort/QSerialPort>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = nullptr);

private:
    QSerialPort *Reader = nullptr;
    QByteArray  *BarCodeBuffer = nullptr;

private slots:
    void    sltReadData (void);

};
#endif // MAINWINDOW_H

#include <QDebug>
#include "mainwindow.h"

MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    BarCodeBuffer = new QByteArray;

    Reader = new QSerialPort;
    Reader->setPortName("COM9");
    Reader->setBaudRate(QSerialPort::Baud115200);
    Reader->setDataBits(QSerialPort::Data8);
    Reader->setParity(QSerialPort::NoParity);
    Reader->setStopBits(QSerialPort::OneStop);
    Reader->setFlowControl(QSerialPort::NoFlowControl);
    qDebug() << Reader->open(QIODevice::ReadWrite);

    if(!Reader->isOpen())
    {
        qDebug() << "Error com9";
    }
    else
    {
        connect(this->Reader, SIGNAL(readyRead()), this, SLOT(sltReadData()));
        Reader->write(QByteArray("R")); //Send reset to BarCode Reader
    }
}


void MainWindow::sltReadData(void)
{
    //Waiting serial data
    if(Reader->bytesAvailable() == 0)
    {
        qDebug() << Reader->bytesAvailable();
        return;
    }

    BarCodeBuffer->append(Reader->readAll());
}

Any suggestion?
Thanks.
Best regards.

Stefano

Christian Ehrlicher

@Stefanoxjx said in Problem with QSerialPort::readyRead signal:

Seems that this signal is called one time, only when connect signal/slot function is executed.

QObject::connect() does not call the slot. It's only called when the signal is emitted. So put a breakpoint in your slot and take a look at the backtrace from where/if it is emitted

Stefanoxjx

Hi Christian,
I explained bad :(
I know that QObject::connect doesn't emit any signal, I wrote this because I saw that the slot is called only one time, immediately after to have connect the signal to the slot.
I already tried to place a breakpoint in my slot

I placed a breakpoint in this slot but when I receive data from serial port this slot is not called.

but after first time, it isn't called anymore.

Stefano

SGaist

Hi,

Might be a silly question but are you sure your device sends more data than what you receive after you sent the reset command ?

Stefanoxjx

Hi SGaist, you're a Genius :)
The problem is the bad command sent to device.

Many thanks for help.