How does QSignalMapper work?

Question

After my post here : Associate signal and slot to a qcheckbox create dynamically I need to associate :

• The signal clicked() when I click on a qC

Answer 1

First I will explain you how QSignalMapper works. Then I will explain you why you don't need it.

How QSignalMapper works:

Create s QSignalMapper. Lets assume that you want to assign an integer value to each checkbox, so every time you click on any checkbox, you will get a signal with the integer value assigned to it.

Connect the mapper signal to your SLOT, that you will implement:

connect(mapper, SIGNAL(mapped(int)), this, SLOT(yourSlot(int)));

Now you can write slot, that will take integer argument. The argument will be different for each checkbox you have.

While you create checkboxes, for each checkbox you need to do following:

mapper->setMapping(checkBox, integerValueForThisCheckbox);
connect(checkBox, SIGNAL(clicked()), mapper, SLOT(map()));

From now on, every time you click on a checkbox, it will emit clicked() signal to the QSignalMapper, which will then map it to the assigned integer value and will emit mapped() signal. You connected to that mapped() signal, so yourSlot(int) will be called with the proper integer value.

Instead of integers, you can assign QString, QWidget* or QObject* (see Qt documentation).

This is how QSignalMapper work.

You don't need it:

• The QTableWidget *monTab is the single object, it doesn't change. Keep it as a class member field and use it from your slot function.
• The QCheckBox *pCheckBox - you can get it by casting sender() to QCheckBox*.

Like this:

void supervision::yourSlot()
{
    QCheckBox* pCheckBox = qobject_cast(sender());
    if (!pCheckBox) // this is just a safety check
        return;
}

The sender() function is from QObject, which you do inherit from, so you have access to it.

• The int linge (it's a line number, right?) - when you create checkboxes, you can store pointers to that checkboxes in QList class field and use it from your slot function find out which line is it, like this:

In class declaration:

private:
    QList checkboxes;

When creating checkboxes:

QCheckBox* cb = new QCheckBox();
checkboxes << cb;

In your slot function:

void supervision::yourSlot()
{
    QCheckBox* pCheckBox = qobject_cast(sender());
    if (!pCheckBox) // this is just a safety check
        return;

    int linge = checkboxes.indexOf(pCheckBox);
}

If you want, you can skip that QList and use QSignalMapper and assign lines to checkboxes using mapper. That's just a matter of what you prefer.