styling text regions with class selector from global QSS - qt

Question

How can I style a span that is part of a widget text (e.g.
a QLabel) via global style sheet?
E.g. in below example, both foo and bar should be red.
#include <QtWidgets/QApplication>
#include <QtWidgets/QLabel>
class
some_label : public QLabel
{
Q_OBJECT
public:
some_label(QString text = "") : QLabel(NULL) {
setText(text);
show();
};
};
#include "main.moc"
static const char *css =
"some_label { color : blue; background : black; }"
"span.some_class { color : red; }";
int
main(int argc, char **argv)
{
QApplication a(argc, argv);
a.setStyleSheet(css);
some_label label("before "
"<span style=\"color:red;\">foo</span> " /* works */
"<span class=\"some_class\">bar</span> " /* fails */
"after");
return a.exec();
}
Qmake (Qt 5.1.1) project file:
QT += widgets
SOURCES += main.cpp
I would really appreciate a solution that avoids hardcoding the style as I did
with the foo span.
The goal is for the application look to be determined entirely by a
user-supplied style sheet (represented by css in the example).
At the moment I use a workaround involving separate labels for each element
that is colored and it is a nightmare to maintain.
I have consulted a few online sources as well as Blanchette/Summerfield chapter
19 but those are primarily concerned with styling whole widgets.

Answer 1

If you don't need to change styling after the QLabel loads, you could devise a system where you text-replace the colors you want for each word from a centralized style file:
// These values come from a central, user-supplied style sheet, etc.
QString primary = "red";
QString secondary = "green";
some_label label("before "
"<font color=\"" + secondary + "\">foo</font> "
"<font color=\"" + primary + "\">bar</font> "
"after");
This system is a little hard to read but it could be an improvement over using many QLabels.
(As you may have noticed, Qt doesn't support CSS selection of classes within QLabels.)