How to connect signal to this member function using the new method?

Tapsa

I based my code on this example:

void someFunction();
QPushButton *button = new QPushButton;
QObject::connect(button, &QPushButton::clicked, someFunction);

In a header file I have:

class MainWindow : public QMainWindow
{
    Q_OBJECT
    ...
private:
    void select_filter(int);
    QComboBox *unit_filters;
};

Then in a source file I have:

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    ...
    unit_filters = new QComboBox;
    QObject::connect(unit_filters, &QComboBox::currentIndexChanged, select_filter);
    // or this
    QObject::connect(unit_filters, &QComboBox::currentIndexChanged, [this]{select_filter(0);});
}
    
void MainWindow::select_filter(int)
{
    ...
}

How can I make it compile? As you can see, I did what the documentation told me.
I am getting 'no matching function' and 'unresolved overload' etc.
I am using Qt Creator 3.6.0 based on Qt 5.5.1.

hskoglund

Hi, you get an error because there are 2 different currentIndexChanged() signals, so you have to tell the compiler which one you want read more here

JordanHarris

Well the example you show is using a free function, not a member function. Perhaps that's why the first connect() doesn't work. In the second, you are missing the empty argument list "()" in the lambda. I believe this should work:

QObject::connect(unit_filters, &QComboBox::currentIndexChanged, this,  &MainWindow::select_filter);
// or this
QObject::connect(unit_filters, &QComboBox::currentIndexChanged,  [this]() { select_filter(0); });

Tapsa

Thank you, hskoglund. I added a cast to the signal.

static_cast<void(QComboBox::*)(int)>(&QComboBox::currentIndexChanged)