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?

score 3 · Answer 1 · edited Aug 14 '18 at 12:07

3

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!

edited Aug 14 '18 at 12:07

AAEM

1,837
2
18
26

answered Jul 15 '13 at 04:00

Jamin Grey

10,151
6
39
52

Can you elaborate? I don't really understand. What would I write the function as? void MainWindow::QButtonGroup::buttonClicked(); – mrg95 Jul 15 '13 at 04:33
@mc360pro It's a signal. You connect it to a slot that takes one of the provided argument types. The passed argument will be the clicked button. If you don't know how to connect signals and slots, there's a tutorial here: http://qt-project.org/doc/qt-5.1/qtcore/signalsandslots.html – Nikos C. Jul 15 '13 at 04:47
Let's just say this, I am sad to say that so far, any signal/slot usage I've been doing is when I right click a button and select "Go to slot." From that point I just add my commands to the function that was created in mainwindow.cpp. So I have no clue how to set up my "own function" without just clicking "go to slot." All I want to do right now is click one of the buttons, and have qDebug tell me what button I clicked. If I can do that I'm set. – mrg95 Jul 15 '13 at 05:56
'Go to slot' doesn't always show all the slots available, and can't be used for everything (imagine dynamically creating widgets on the fly - how will you connect the slots of the widgets that don't exist yet?). You need to use 'connect()' to connect signals and slots - I updated my answer just a little, to give an idea of the usage. – Jamin Grey Jul 15 '13 at 16:05

score 3 · Accepted Answer · answered Jul 15 '13 at 07:54

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

How to tell when a QPushButton is clicked in a QButtonGroup

2 Answers2