CSS class selector not working with container widgets

[ashbob999]

Using QT5.15.2 msvc 32-bit.

I have a window which contains the following structure:

QMainWindow
---> QWidget
-------> QTabWidget
-----------> QComboBox

Where the QWidget has a class property (class="className").
Styling the QCombox only works correctly if it is created dynamically.

Using the following css, the drop-down menu of the QComboBox only shows yellow if it is created dynamically.

.className QComboBox QAbstractItemView {
    background-color: yellow;
}

Code to create QComboBox dynamically:

QComboBox* box = new QComboBox();
box->addItem("a");
box->addItem("b");
this->ui->tabWidget->currentWidget()->layout()->addWidget(bx2);

But any QComboBox that is inside the QWidget but not in the QTabWidget is styled correctly. Or if I remove the .className selector from the css.

So it seems like a problem with QTabWidget, and having .className and QAbstractItemView on the same css statement.

[ashbob999]

After some testing it seems that because in the ui file the class properties are set after all the widgets are created and added, the QComboBoxListView private class's style does not get updated.

But if the class properties are added straight after the widget is created, the it is styled correctly.

Ui file from:

void setupUi(...) {
    widget = new QWidget(...);
    comboBox = new QComboBox(widget);

    ...

    retranslateUi(MainWindow); // sets class properties
}

To

void setupUi(...) {
    widget = new QWidget(...);
    widget.setProperty("class", "test"); // coptied from restranslateUi function
    comboBox = new QComboBox(widget);

    ...

    retranslateUi(MainWindow); // sets class properties
}

Obviously this is not a usable solution because the ui_*.h file is auto generated.

Another way to fix this is to re-polish the QComboBoxListView by recursively re-polishing QComboBox and it's children

void recursively_polish(QObject* object) {
    auto* widget = dynamic_cast<QWidget*>(object);
    if (widget!=nullptr){
        widget->style()->unpolish(widget);
        widget->style()->polish(widget);
    }

    auto children = object->findChildren<QObject*>(QString(), Qt::FindDirectChildrenOnly);
    for (auto& child : children){
        polish_recursive(child);
    }
}

Is this the only way to fix it, or is there another better way?

[JonB]

@ashbob999
I had been going to ask what you had done about polishing, given your behaviour, but you have answered. So far as I know this is indeed required/best/simplest, see discussion Is there a better method than calling polish recursively on all children of a QWidget?

[ashbob999]

@JonB Thats fine, at least I don't have to unpolish first.
Although I still think there is a bug because you don't have to polish the QComboBox's ItemView when it is not inside a QTabWidget or QStackedWidget.