How to connect signal and slot with another object in qt --solved - c++

Question

I am doing a qt project, my goal is to draw something based on my input. The signal is in the main, and the drawing is in another object, I am not able to connect them.
int main(int argc, char *argv[])
{
QApplication app(argc, argv);
Frequency fre; //this is the class that does the drawing
QWidget *window = new QWidget;
QGridLayout *grid = new QGridLayout;
QGroupBox *groupBox = new QGroupBox(QObject::tr("Volume"));
QSpinBox *spinBox = new QSpinBox;
spinBox->setRange(0, 5);
QObject::connect(spinBox, SIGNAL(valueChanged(int)),&fre, SLOT(setVolume(int)));
QVBoxLayout *Vbox = new QVBoxLayout;
Vbox->addWidget(spinBox);
groupBox->setLayout(Vbox);
grid->addWidget(groupBox, 4,7,1,1);
window->setLayout(grid);
window->show();
return app.exec();
}
This is how I set up the Frequency class :
in h file
class Frequency : public QGLWidget
{
Q_OBJECT
public slots:
void setVolume(int value);
in cpp file
void Frequency :: setVolume(int val) {
vol = val;
updateGL();
}
void Frequency :: paintGL() {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
draw();
}

Answer 1

Since I can't put all this in the comment section, I'm going to put it here:
I copied your code and I'm not able to reproduce the error with Qt version 5.14.0, because when I change the value in any way, the method, void MyObject::setVolume(int value) is being called.
This code should work for you. Possibly, you are running it in release mode, and used a breakpoint to check if it was called (which doesn't always work on release mode).
// #include "QtWidgetsApplication4.h"
#include <QtWidgets/QApplication>
#include "MyObject.h"
#include <QGridLayout>
#include <QGroupBox>
#include <QSpinBox>
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
// QtWidgetsApplication4 w;
// w.show();
// return a.exec();
MyObject object;
QWidget* window = new QWidget;
QGridLayout* grid = new QGridLayout;
QGroupBox* groupBox = new QGroupBox(QObject::tr("Volume"));
QSpinBox* spinBox = new QSpinBox;
spinBox->setRange(0, 5);
QObject::connect(spinBox, SIGNAL(valueChanged(int)), &object, SLOT(setVolume(int)));
QVBoxLayout* Vbox = new QVBoxLayout;
Vbox->addWidget(spinBox);
groupBox->setLayout(Vbox);
grid->addWidget(groupBox, 4, 7, 1, 1);
window->setLayout(grid);
window->show();
return a.exec();
}
#pragma once
#include <QObject>
class MyObject : public QObject
{
Q_OBJECT
public slots:
void setVolume(int value);
private:
int m_volume;
};
#include "MyObject.h"
void MyObject::setVolume(int value)
{
m_volume = value;
}