QComboBox doesn't works change event

[MyNameIsQt]

Change item event on combo box doesn't work.
If you look up a YouTube video, it shows selecting a combobox item and pressing a button.
Doesn't signal work when changing combobox item?
If so, why am I not working?
As a test, I made a push button and added a click signal event. But this also doesn't work.

void ResizeDlg::on_comboWidthSize_currentIndexChanged(int index)
{
 qDebug() << "test";
  ....
}

void ResizeDlg::on_pushButton_clicked()
{
    qDebug() << "test";
}

[JonB]

@MyNameIsQt
It should. Do you mean nothing happens at runtime when you do the action? (In fact because of how it's named and you have auto-connections enabled, it should get invoked twice). Both of your cases should. Start from these:

connect(ui->comboWidthSize, &QComboBox::currentIndexChanged, this, &ResizeDlg::on_comboWidthSize_currentIndexChanged);
connect(ui->pushButton, &QPushButton::clicked, this, &ResizeDlg::on_pushButton_clicked);

connect(ui->comboWidthSize, &QComboBox::currentIndexChanged, this, []() { qDebug() << "QComboBox::currentIndexChanged"; } );
connect(ui->pushButton, &QPushButton::clicked, this, []() { qDebug() << "QPushButton::clicked"; } );

[Christian Ehrlicher]

Please do not use the auto-connect stuff but connect the signals and slots by yourself. I would guess the name of your combobox is not comboWidthSize

[MyNameIsQt]

@Christian-Ehrlicher
Did you mean this?

ResizeDlg::ResizeDlg(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::ResizeDlg)
{
    ui->setupUi(this);

    QStringList widthSizeOpt;
    widthSizeOpt << "Percent" << "Inches" << "Centimeters" << "Millimeters";
    ui->comboWidthSize->addItems(widthSizeOpt);
    ui->comboWidthSize->setCurrentIndex(2);
    QStringList heightSizeOpt;
    heightSizeOpt << "Percent" << "Inches" << "Centimeters" << "Millimeters";
    ui->comboHeightSize->addItems(heightSizeOpt);
    ui->comboHeightSize->setCurrentIndex(2);

    QObject::connect(ui->comboWidthSize, SIGNAL(currentIndexChanged(int)), this, SLOT(on_comboWidthSize_currentIndexChanged(int)));
}

But this doesn't work!

[JonB]

@MyNameIsQt
It should. Do you mean nothing happens at runtime when you do the action? (In fact because of how it's named and you have auto-connections enabled, it should get invoked twice). Both of your cases should. Start from these:

connect(ui->comboWidthSize, &QComboBox::currentIndexChanged, this, &ResizeDlg::on_comboWidthSize_currentIndexChanged);
connect(ui->pushButton, &QPushButton::clicked, this, &ResizeDlg::on_pushButton_clicked);

connect(ui->comboWidthSize, &QComboBox::currentIndexChanged, this, []() { qDebug() << "QComboBox::currentIndexChanged"; } );
connect(ui->pushButton, &QPushButton::clicked, this, []() { qDebug() << "QPushButton::clicked"; } );

[MyNameIsQt]

@JonB

.h file

#include <QComboBox>
class ResizeDlg : public QDialog
{
private slots:
    void convertPixel();
    void convertSize();
...
}

.cpp file

ResizeDlg::ResizeDlg(QWidget *parent)
    : QDialog(parent)
    , ui(new Ui::ResizeDlg)
{
    ui->setupUi(this);

    connect(ui->comboWidth, SIGNAL(currentIndexChanged(int)), this, SLOT(convertPixel()));
    connect(ui->comboWidthSize, SIGNAL(currentIndexChanged(int)), this, SLOT(convertSize()));
}

void ResizeDlg::convertPixel()
{
    QMessageBox::information(nullptr, "test", "text.");
    qDebug() << "Hello";
}

void ResizeDlg::convertSize()
{
       QMessageBox::information(nullptr, "test", "text.");    
        qDebug() << "Hello";    
}

Application Output

qt.core.qobject.connect: QObject::connect: No such slot QDialog::convertPixel() in ..\WpubViewer\resizedlg.cpp:33
qt.core.qobject.connect: QObject::connect:  (sender name:   'comboWidth')
qt.core.qobject.connect: QObject::connect:  (receiver name: 'ResizeDlg')
qt.core.qobject.connect: QObject::connect: No such slot QDialog::convertSize() in ..\WpubViewer\resizedlg.cpp:34
qt.core.qobject.connect: QObject::connect:  (sender name:   'comboWidthSize')
qt.core.qobject.connect: QObject::connect:  (receiver name: 'ResizeDlg')

Why does this message occur?

[MyNameIsQt]

@JonB Thanks. It was solved thanks to you.
:)

  connect(ui->comboWidthSize, &QComboBox::currentIndexChanged, this, &ResizeDlg::convertPixel);
    connect(ui->comboWidth, &QComboBox::currentIndexChanged, this, &ResizeDlg::convertSize);

[JonB]

@MyNameIsQt
I am glad you have changed over to the Qt New Signal Slot Syntax, which was brought in a decade ago. I recommend you now use this and no longer SIGNAL/SLOT() macros going forward.

[Christian Ehrlicher]

@MyNameIsQt said in QComboBox doesn't works change event:

Why does this message occur?

Because you did not add the Q_OBJECT macro

[JonB]

@Christian-Ehrlicher
Ah, I didn't know that must apply with old-style connect. I nearly mentioned this to user, but it seems it all works with new-style syntax. My understanding is you need Q_OBJECT if you emit signals, but you can get away without if you only connect/use slots, right?

[Christian Ehrlicher]

@JonB said in QComboBox doesn't works change event:

My understanding is you need Q_OBJECT if you emit signals, but you can get away without if you only connect/use slots, right?

No, you need it when you want qobject_cast<> or old style connect or any other QMetaObject feature.

[JonB]

@Christian-Ehrlicher
I cannot test, but I thought if you have

signals:
    void someSignal();

you also need Q_OBJECT else you get some moc error or something?

[Christian Ehrlicher]

@JonB Maybe a linker error (vtable) - don't know.