如何在其他类的嵌套循环内进入主事件循环QCoreApplication来实现网络操作？

Question

This post is similar to the first one I posted, but I made some changes and I understand what is wrong. The error lies in event loop QCoreApplication that is not called within the nested loops and consequently the networking events are not met. My problem is always to send a json to my API Rest. This is the tour that is my code: the main class that calls the SerialReader laws of bytes from the serial port, identifies if the package is right and if it sends the Parser class that divides the various bytes and then sending those required API

This is my main.cpp

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);
    SerialReader serialReader;
    QTimer::singleShot(0, &serialReader, SLOT(runSerialReader()));
    ...
    return a.exec();
}

This is my serialreader.cpp / serialreader.h

/*serialreader.h*/
class SerialReader : public QObject
{
    Q_OBJECT

...
public:
    void processData(QByteArray datas);

public slots:
    void runSerialReader();
private:
    Parser parser;
...
};

/*serialreader.cpp*/
SerialReader::SerialReader() {}

void SerialReader::runSerialReader(){
    ...
    if (serialPort->isOpen())
    {
        qDebug() << "Serial port is open...";
        while (serialPort->waitForReadyRead(50))
        {
            QByteArray datas = serialPort->readAll();
            if (datas.size() == 0){
                qDebug() << "ERROR data not read";
            } else {
                processData(datas);
            }
        }
    } else {
        qDebug() << "OPEN ERROR: " << serialPort->errorString();
    }

    serialPort->close();
    qDebug() << "...serial port is closed!";
    ...
}

void SerialReader::processData(QByteArray datas)
{
    for (int i = 0; i < datas.size(); i++)
    {
        switch (state)
        {
        ...
        case EXIT:
            ...
            parser.setPackage(serialBuffer);
            ...
        }
    }
 }

This is my parser.cpp / parser.h

/*parser.h*/
class Parser : public QObject
{
    Q_OBJECT

public:
    ...
    QQueue<QByteArray> queue;
    void setPackage(QByteArray &serialBuffer);
    void sendPacketToAPI(QByteArray &bufferToPacket);

public slots:
   void replyFinished(QNetworkReply *reply);

private:
    QNetworkAccessManager *m_manager;
    quint8 m_a;
    quint8 m_b;

}

/*parser.cpp*/
Parser::Parser()
    : m_manager { new QNetworkAccessManager }
{
    connect(m_manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(replyFinished(QNetworkReply*)));
}

void Parser::setPackage(QByteArray &serialBuffer){
    ...
    bufferToPacket.append(bufferToParse.at(i));
    ...
}

void Parser::replyFinished(QNetworkReply *reply)
{
    reply->deleteLater();
    qDebug() << "~error " << reply->errorString();
    qDebug() << "reply delete!";
    qDebug() << "https post_request done!";
}

void Parser::sendPacketToAPI(QByteArray &bufferToPacket){
    m_a = bufferToPacket.at(0);
    m_b = bufferToPacket.at(1);
    QNetworkRequest request;
    request.setUrl(QUrl ("http://..."));
    request.setHeader(QNetworkRequest::ContentTypeHeader, "application/json");
    QString json = QString("{\"a\":\"%1\",\"b\":\"%2\"}").arg(m_a).arg(m_b);

    m_manager->post(request, json.toUtf8()); 
    QCoreApplication :: processEvents (QEventLoop :: AllEvents);
}

In practice after entering the serial reader read in continuation of bytes so as to become an infinite loop and are therefore always recalled all nested methods. I tried to solve the problem with the static method QCoreApplication::processEvents(QEventLoop::AllEvents) but I can not play the main loop QCoreApplication. How can I do?

Answer 1

Calling QCoreApplication::processEvents does not seem to be a good solution and with little refactoring you won't need it. Qt gives you two options to handle serial port. You can use either blocking API or async API of QSerialPort . However when using blocking API (as you are doing when calling waitForReadyRead() ) you should move code that reads serial data to some worker thread to not block the main event loop. The other option is to use async API and connect to readyRead() signal to process incoming data.

In your case it is probably easier to do modify SerialReader class and replace while(...) loop with asynchronous processing of incoming data in a slot connected to readyRead() signal.

There are good examples for QSerialPort http://doc.qt.io/qt-5/qtserialport-examples.html