How to setStyleSheet for QLabel in a specific class in Qt - qt

Question

I have a testing sample like this:In class B, which only has a QVector to store some QLabel like this:
class B : public QWidget
{
public:
B(QWidget *parent = 0);
QVector<QLabel*> mLbls;
};
And in class A, I have the following code:
A::A(QWidget *parent)
: QMainWindow(parent)
{
QWidget *mWidget = new QWidget(this);
QHBoxLayout *hLayout = new QHBoxLayout(mWidget);
B testingB;
testingB.mLbls.resize(5);
for(int i = 0; i < 5; i++) {
testingB.mLbls[i] = new QLabel(mWidget);
testingB.mLbls[i]->setText(QString::number(i));
hLayout->addWidget(testingB.mLbls[i]);
}
setStyleSheet("QLabel {background-color: red;}"); //I want to set the QLabel bg color to red
mWidget->setLayout(hLayout);
setCentralWidget(mWidget);
}
So what I am trying to do is set all QLabel that ONLY in Class B to red color. But the problem is, if I use setStyleSheet("QLabel {background-color: red;}");, all the QLabel(even the QLabel in Class A) will be set to red background color.
I do not know how to set all the stylesheet only for CLass B object. And I know I could use this way to implement what I am trying to do:
for(int i = 0; i < 5; i++) {
testingB.mLbls[i] = new QLabel(mWidget);
testingB.mLbls[i]->setText(QString::number(i));
testingB.mLbls[i]->setStyleSheet("QLabel {background-color: red;}"); //new added
hLayout->addWidget(testingB.mLbls[i]);
}
By using that way, I think that so troublesome to set stylesheet for them one by one individually, besides sometimes I may need to set some QLabel stylesheet differently and the rest of them just have the same stylesheet. If I have more objects and set each of them one by one, that may cost a lot of time.So I assume there is a way to set stylesheet for some objects in a class once for all. Hope that I explain my question clearly. To solve that problem, what can I do? Thanks.

Answer 1

Qt CSS syntax allows you to select children for the CSS rules (Qt doc), but it is based on the parentship of QObjects not in which class contains pointers to the QLabel.
This CSS will only apply to QLabel objects which are children or grand children of a YourContainerClassWidget object.
// C++
auto container = new YourContainerClassWidget;
auto label = QLabel(container); // The label is now a child of container
// CSS
YourContainerClassWidget QLabel { // Descendant selector
background-color: red;
}
// You can also apply only to direct children with this syntax
YourContainerClassWidget > QLabel { // Child selector
background-color: red;
}