How many pixels do items in QComboBox need? - c++

Question

I would like to know how many pixels need this items in QComboBox:
red - checkbox
green - distance between end of checkbox and beggining of the text
blue - distance between end of border and beggining of the checkbox
In doc of QStyle I find two methods:
subElementRect()
pixelMetric()
I think I have to use them, but I don't know, which args I need to use.

Answer 1

It depends on the style.
QCommonStyle for example draws the ComboBox's label like this:
if (const QStyleOptionComboBox *cb = qstyleoption_cast<const QStyleOptionComboBox *>(opt)) {
QRect editRect = proxy()->subControlRect(CC_ComboBox, cb, SC_ComboBoxEditField, widget);
p->save();
p->setClipRect(editRect);
if (!cb->currentIcon.isNull()) {
QIcon::Mode mode = cb->state & State_Enabled ? QIcon::Normal
: QIcon::Disabled;
QPixmap pixmap = cb->currentIcon.pixmap(qt_getWindow(widget), cb->iconSize, mode);
QRect iconRect(editRect);
iconRect.setWidth(cb->iconSize.width() + 4);
iconRect = alignedRect(cb->direction,
Qt::AlignLeft | Qt::AlignVCenter,
iconRect.size(), editRect);
if (cb->editable)
p->fillRect(iconRect, opt->palette.brush(QPalette::Base));
proxy()->drawItemPixmap(p, iconRect, Qt::AlignCenter, pixmap);
if (cb->direction == Qt::RightToLeft)
editRect.translate(-4 - cb->iconSize.width(), 0);
else
editRect.translate(cb->iconSize.width() + 4, 0);
}
if (!cb->currentText.isEmpty() && !cb->editable) {
proxy()->drawItemText(p, editRect.adjusted(1, 0, -1, 0),
visualAlignment(cb->direction, Qt::AlignLeft | Qt::AlignVCenter),
cb->palette, cb->state & State_Enabled, cb->currentText);
}
p->restore();
}
This means, that the actual size of the icon's rectangle can be determined by subclassing QComboBox (to access its protected initStyleOption method) and creating a new public getIconRect method in the following way:
QRect ComboBox::getIconRect()
{
QStyleOptionComboBox opt;
initStyleOption(&opt);
QRect rect(style()->subControlRect(QStyle::CC_ComboBox, &opt, QStyle::SC_ComboBoxEditField));
rect.setWidth(opt.iconSize.width() + 4);
return rect;
}
Then in MainWindow for example create a ComboBox and call its getIconSize method like this:
auto *cmbBox = new ComboBox(this);
qDebug() << cmbBox->getIconRect();
For me, on Windows 10, this gives:
QRect(3,3 20x14)
There could be other ways, but if you insist on using a method similar to QStyle::subControlRect, those are the correct arguments;