A simple connection error

qcoderpro

The question is for this connection:

#include <QApplication>
#include <QHBoxLayout>
#include <QSlider>
#include <QSpinBox>

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

    QWidget *window = new QWidget;
    window->setWindowTitle("Enter Your Age");

    QSpinBox *spinBox = new QSpinBox;
    QSlider *slider = new QSlider(Qt::Horizontal);
    spinBox->setRange(0, 130);
    slider->setRange(0, 130);

    QObject::connect(spinBox, &QSpinBox::valueChanged, slider, &QSlider::setValue);
...

I get this error for the connection, but I cannot understand it well:
error: no matching function for call to 'QObject::connect(QSpinBox&, <unresolved overloaded function type>, QSlider*&, void (QAbstractSlider::)(int))'
QObject::connect(spinBox, &QSpinBox::valueChanged, slider, &QSlider::setValue);
^

Bonnie

@qcoderpro
It is in the Obsolete Members :)

Pablo J. Rogina

@qcoderpro it looks like documentation is your friend in this case (signal valueChanged is overloaded in QSpinBox)

qcoderpro

@Pablo-J-Rogina

Don't understand this either!
Here both QSplineBox and QSlider have one valueChanged/setValue respectively with one parameter of type int. Everything looks matched. Can't find the clue for the problem yet.

Bonnie

@qcoderpro
Actually QSpinBox has two valueChanged signals:

void valueChanged(int i)
void valueChanged(const QString &text)

qcoderpro

@Bonnie

Where is the QString based one? I only found the int based: https://doc.qt.io/qt-5/qspinbox-members.html

Bonnie

@qcoderpro
It is in the Obsolete Members :)

qcoderpro

@Bonnie
Ow, found, thanks, solved.

qcoderpro

Another connection problem:

"dialogTest.h":

#ifndef DIALOGTEST_H
#define DIALOGTEST_H

#include <QDialog>

class QPushButton;
class QLineEdit;
class dialogTest : public QDialog
{
    Q_OBJECT

public:
    dialogTest(QWidget *parent = nullptr);
    ~dialogTest();

private:
    QPushButton* button;
    QLineEdit* lineEdit;
};
#endif // DIALOGTEST_H

"dialogTest.cpp":

#include "dialogtest.h"
#include <QPushButton>
#include <QLineEdit>
#include <QHBoxLayout>
#include <QVBoxLayout>

dialogTest::dialogTest(QWidget *parent)
    : QDialog(parent)
{
    button = new QPushButton(tr("Close"));
    lineEdit = new QLineEdit;

    QHBoxLayout* hLayout = new QHBoxLayout;
    hLayout->addWidget(lineEdit);
    hLayout->addWidget(button);

    setLayout(hLayout);

   connect(button, &QPushButton::clicked, &QDialog, &QDialog::close);
}

dialogTest::~dialogTest()
{
    delete button;
    delete lineEdit;
}

I get this error: error: expected primary-expression before ',' token
connect(button, &QPushButton::clicked, &dialogTest, &dialogTest::close)

Even when I use this instead:

connect(button, &QPushButton::clicked, &dialogTest, &dialogTest::close);

I get the same error: error: expected primary-expression before ',' token
connect(button, &QPushButton::clicked, &dialogTest, &dialogTest::close);

Bonnie

@qcoderpro
The third parameter should be a pointer.
So "& + ClassName" is not a valid expression.
You should use "this".

qcoderpro

@Bonnie

So an address is not accepted and should it exactly be a pointer!? Why?

And that this you used is actually a pointer to the object we've created in main.cpp, right?

Bonnie

@qcoderpro
An address to an QObject object is acceptable. But I don't think "& + ClassName" is an address. It is not a valid expression at all.
And I haven't seen your main.cpp with a dialogTest, so I'm not sure.
But isn't "this" very basic in C++ class knowledge?

qcoderpro

@Bonnie

Yeah, a pointer varies from an address.

This is my main.cpp:

#include "dialogtest.h"

#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    dialogTest w;
    w.show();
    return a.exec();
}

So the "this" you used is the pointer to the object, here "w", as the top-level widget of the project. Is it right?

Bonnie

@qcoderpro
Yeah, using "this" inside dialogTest equals "&w".