Static slot function

Everdream

Hello,

I'm trying to connect a QButtonGroup signal with a static slot function like this:

QObject::connect(ui->ModeGroup, SIGNAL(buttonClicked(int)),SLOT(module::toggle_mode(int)));

But the slot does not answer to the signal.

I tried that too:

QObject::connect(ui->ModeGroup, &QButtonGroup::buttonClicked,&module::toggle_mode);

This version gave me an error when compiling. I might think that is looking for a slot function with a QPushButton* as input. But i'd like to use the overload buttonClicked(int) signal.

The error I got from the last method is:

mainwindow.cpp:65:18: error: no matching member function for call to 'connect'
qobject.h:463:41: note: candidate function not viable: no overload of 'buttonClicked' matching 'const char *' for 2nd argument
qobject.h:260:13: note: candidate template ignored: couldn't infer template argument 'Func1'
qobject.h:300:13: note: candidate template ignored: couldn't infer template argument 'Func1'
qobject.h:228:43: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
qobject.h:269:13: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
qobject.h:308:13: note: candidate function template not viable: requires at least 4 arguments, but 3 were provided
qobject.h:208:36: note: candidate function not viable: requires at least 4 arguments, but 3 were provided
qobject.h:211:36: note: candidate function not viable: requires at least 4 arguments, but 3 were provided

Is my writting wrong?

By the way, I'm using Qt 5.12.8.

Thanks,

Eve

jsulm

@Everdream said in Static slot function:

buttonClicked

Proper signature of the signal is

void QButtonGroup::buttonClicked(QAbstractButton*)

not

void QButtonGroup::buttonClicked(int)

I don't think you can use a static method as slot. Also, why do you want to do so?

Everdream

Well, when I do that:
QObject::connect(ui->ModeGroup, SIGNAL(buttonClicked(int)),scvG,SLOT(toggle_mode(int)));

Using an instance pointer of the **module ** class, it's working. There is an overload method of buttonClicked with the int ID of the button clicked.

I put it static since the attribut modified by the slot is also static.

I think, it's kinda weird to mention a pointer to an instance to modify a static variable.

Well, I think, I'll go for that. At least it's working.

JonB

@Everdream
If you are having problems with a static function as a slot, connect it via a lambda. Though e.g. https://stackoverflow.com/questions/9428038/is-it-possible-to-connect-a-signal-to-a-static-slot-without-a-receiver-instance shows you that you can anyway.

Also, why are you now going back to old-style signal/slot connections when you started out using the much better new-style? You will be better served if you always stick to new-style.

J.Hilk

@Everdream said in Static slot function:

I think, it's kinda weird to mention a pointer to an instance to modify a static variable.

you shouldn't,

this for example works fine

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

    QTimer *t(new QTimer(Q_NULLPTR));
    QObject::connect(t, &QTimer::timeout, &myWidget::testFunction);
    t->start(200);


    return app.exec();
}

class myWidget : public QWidget
{
    Q_OBJECT
public:
    myWidget(QWidget * parent = nullptr) : QWidget(parent){
    }


    static void testFunction() {qDebug() << "TestPrint "<< QTime::currentTime();}

};

Everdream

Ok I found a solution to get it working:

QObject::connect(ui->ModeGroup, qOverload<int>(&QButtonGroup::buttonClicked),&module::toggle_mode);

Since the buttonclicked is overloaded signal. It was always trying to connect with the other buttonClicked(QAbstractButton*), qOverload here forced the use of the right signal.

@JonB I tried your other solution, with the lambda function, I didn't succeed to make it work.

Thank you everyone.

You can make the post as solved.

JonB

@Everdream said in Static slot function:

@JonB I tried your other solution, with the lambda function, I didn't succeed to make it work.

Up to you, lambdas do work. But if you have a solution without you don't need them, just bear in mind for next time.

Pablo J. Rogina

@Everdream said in Static slot function:

Ok I found a solution to get it working:

great, and thank you for sharing it. Please don't forget to mark your post as solved then.