How to tell when a QPushButton is clicked in a QButtonGroup

Question

In my project, I have 40 QPushButtons all put into a QButtonGroup like this:

QButtonGroup* group = new QButtonGroup(this);
group->addButton(ui->slot_0);
group->addButton(ui->slot_1);
//...
group->addButton(ui->slot_38);
group->addButton(ui->slot_39);

Each button is a QPushButton that I made checkable. That way only one button can be checked at a time. All works great, but how can I "make a slot" when one of the buttons becomes checked? I don't want to have 40 different slots, one for each button all to end up doing essentially the same thing. Is there any way I can just use the QButtonGroup I put them in?

Answer 1

As Jamin and Nikos stated: you should create your own slot to handle the signal emitted by QButtonGroup. It could be something like this:

In the header file:

public slots:

void buttonWasClicked(int);

In the *.cpp file:

void MainWindow::buttonWasClicked(int buttonID)
{
    cout << "You have clicked button: " << buttonID << endl;
}

And in the code responsible for creation of the MainWindow (i.e. in constructor but not necessairly) there should be this line:

    connect(group, SIGNAL(buttonClicked(int)), this, SLOT(buttonWasClicked(int)));

Be aware that since Qt5 the connect syntax has changed. The syntax I used here is from Qt4. It still works but is deprecated now (for more information please refer to New Signal Slot Syntax in Qt 5). Moreover I would suggest going through QButtonGroup class reference as there are other available signals which could suit your needs better than the one I've chosen.

BR

Answer 2

The documentation for QButtonGroup shows a QButtonGroup::buttonClicked() signal - have you already tried that one?

The signal comes in two variants - one that gives the QPushButton as a parameter (as a QAbstractButton), and one that gives the ID of the button in the group.

You can use connect() to setup signal and slot connections in your C++ code.

Sometime during the initialization of your window's class (perhaps in the constructor), call this:

connect(myButtonGroup, SIGNAL(buttonClicked(QAbstractButton*)), this, SLOT(theSlotThatYouWrite(QAbstractButton*));

Where myButtonGroup is probably this->ui->nameOfTheButtonGroup, and theSlotThatYouWrite is a function that you write in your own code, that belongs to your window's class, that returns void and takes a signal QAbstractButton* as a parameter (since that's what this specific signal gives as an argument).

Make sure theSlotThatYouWrite is under the label "private slots:" or "public slots:" in your class's interface.

Here's a screenshot of actual usage of some signals and slots in my own code.

Signals and Slots is something very important to learn, but can be bit of a hill to climb when first trying to understand it!