How to limit the number of QCheckboxes checked at the same time? - qt

Question

I'm in the process of creating a QT application which is using multiple (14) qcheckboxes. I need to have a limit (preferably set as a variable that i can change) to the number of checkboxes that can be checked at the same time, is there any way to achieve this cleanly ? Thanks for your time.

Answer 1

There is no simple way of doing this, you have to write your code to do it.
I suppose you have the checkboxes in some parent widget class. So I would create a slot which looks like this.
void SomeParentWidget::onCheckBoxToggled(bool value)
{
// when we unchecked the checkbox,
// we do not need to count the number of checked ones
if (!value)
return;
int total = 0;
int limit = 15; // your "magic" number of maximum checked checkboxes
for (auto chb : allCheckBoxes()) // allCheckBoxes() is some method which returns all the checkboxes in consideration
{
if (chb->isChecked())
{
++total;
if (total > limit)
{
// too many checkboxes checked! uncheck the sender checkbox
// Note: you may want to add some nullptr checks or asserts to the following line for better robustness of your code.
qobject_cast<QCheckBox*>(sender())->setChecked(false);
return;
}
}
}
}
And when creating each of your checkboxes inside some parent widget, connect this slot to their signal:
auto chb = new QCheckBox();
connect(chb, &QCheckBox::toggled, this, &SomeParentWidget::onCheckBoxToggled);
Implementation of allCheckBoxes() is up to you, I do not know how you can retrieve the collection of all your check boxes. Depends on your design.

Answer 2

I found another, even simpler solution. Use this slot.
void SomeParentWidget::onCheckBoxToggled(bool value)
{
static int totalChecked = 0; // static! the value is remembered for next invocation
totalChecked += value ? 1 : -1;
Q_ASSERT(totalChecked >= 0);
int maxChecked = 15; // any number you like
if (value && totalChecked > maxChecked)
{
qobject_cast<QCheckBox*>(sender())->setChecked(false);
}
}
... and connect it to checkboxes' toggled() signal. Note that in order to work correctly, all check boxes must be unchecked at the time when you make the signal-slot connection because this function starts counting from zero (0 is the initial value of the static variable).

Answer 3

You can store all your checkboxes in a map (either in an std::map, an std::unordered_map or an QMap). Your keys will be your checkboxes, and your values will be their states, so something like this:
std::unordered_map<QCheckBox*, bool> m_checkBoxStates;
Here's what your connected to your toggled signal of all your checkboxes look like (keep in mind that all the signals will be connected to the same slot):
void MainWindow::onToggled(bool checked) {
QCheckBox* checkBox = sender(); //the checkbox that has been toggled
m_checkBoxStates[checkBox] = checked;
if (!checked) {
return;
}
const int count = std::count_if(m_checkBoxStates.begin(), m_checkBoxStates.end(),
[](const auto pair) {
return pair.second == true;
});
if (count > maxCount) {
checkBox->setChecked(false);
}
}