how to run even of custom c++ function on close event

[shokarta]

Hello, let say I have this:

main.cpp:

#include <QQmlApplicationEngine>
#include <QGuiApplication>
#include <QtQml>
#include <QCoreApplication>
#include <QtCore>
#include "led.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    qmlRegisterType<LED>("LED", 1, 0, "LED");

    const QUrl url(QStringLiteral("qrc:/main.qml"));
    engine.load(url);

    return app.exec();
}

led.h:

#ifndef LED_H
#define LED_H

#include <QObject>
#include <QSerialPort>

class LED : public QObject
{
    Q_OBJECT

public:
    explicit LED(QObject *parent = nullptr);
    Q_INVOKABLE void setColor(int red, int green, int blue);

public slots:

private:

signals:

};

#endif // LED_H

led.cpp:

#include "led.h"
#include <QSerialPort>
#include <QSerialPortInfo>
#include <QtSerialPort/QSerialPort>


namespace Stuff
{
    struct ByteArray: public QByteArray
    {
        ByteArray(std::initializer_list<unsigned char> lst)
            : QByteArray(reinterpret_cast<char const *>(lst.begin()), lst.size())
        {}
    };
}

QSerialPort m_serial;
QString m_port = "COM3";

LED::LED(QObject *parent) :
    QObject(parent)
{
}

void LED::setColor(int red, int green, int blue)
{
	SOME STUFF WHICH IS NOT IMPORTAN HERE
}

and what I need is on close event (alf+f4, hitting the "x" etc) to run function LED::setColor(0,0,0)
where whould be the best place to do this? I have blindly tried to place the LED:::setColor(0,0,0) bellow the return app.exec(); however this is quite nonsence, and also LED::setColor() is not recognized there…

can you please advice how to modify the LED::setColor() in order to be recognized? and where is the best place to place this onClose() event script?

Thank you

[J.Hilk]

@shokarta
you could try:

//needs include of QCoreApplication
#include <QCoreApplication>
LED::LED(QObject *parent) :
    QObject(parent)
{
    connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, this, [=]()->void{setColor(0,0,0)});
}

if it's too late, you probably have to hook into the event system to prevent the close first

[shokarta]

led.cpp:32:108: error: expected ';' after expression
on that line with:
connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, this, =->void{setColor(0,0,0)});
not sure why, to me syntax looks ok :(

[J.Hilk]

@shokarta sorry my bad I wrote without an editor:

connect(QCoreApplication::instance(), &QCoreApplication::aboutToQuit, this, [=]()->void{setColor(0,0,0);});

it needs a ; after the setColor