QApplication Stylesheet completely breaks QGraphicsProxyWidget

[Pekoyo]

Regardless of the different combination of flags or cache mode in

GUI::Graphics_Widget::Graphics_Widget(QWidget* widget, QGraphicsItem* parent) :
	QGraphicsProxyWidget(parent)
{
	setWidget(widget);
	setFlag(QGraphicsItem::ItemIsMovable);
	setFlag(QGraphicsItem::ItemIsFocusable);
	setCacheMode(QGraphicsItem::ItemCoordinateCache);
	setFocusPolicy(Qt::StrongFocus);
}

As soon as the global stylesheet applied to the application instance has any entry, the widgets inside the Proxy cannot be interacted with anymore, eg (QLineEdit, QComboBox, etc...).

Example:
If the stylesheet is "QPushButton { background: red; }", it breaks the proxy / interaction.
If the stylesheet is "", it works again.

void GUI::GraphicsView::mousePressEvent(QMouseEvent* event) {
    if (auto item = scene->itemAt(mapToScene(event->pos()), transform())) {
	if (QGraphicsProxyWidget* proxyWidget = qgraphicsitem_cast<QGraphicsProxyWidget*>(item)) {
            // NEITHER
	    QApplication::sendEvent(proxyWidget->widget(), event);
            // OR
	    QApplication::sendEvent(proxyWidget, event);
            // WORK (they are being properly called but the QComboBox does not expand)
	}
    }
    QGraphicsView::mousePressEvent(event);
}

[SGaist]

Hi,

Which version of Qt ?
On which OS ?
Can you provide a minimal compilable example that shows this behavior ?

[Pekoyo]

Sorry, of course
Qt 6.8.3 (6.8.3_msvc2022_64)
Windows 11

Basically as long as there is any stylesheet applied it breaks.
(Commenting out or doing: app->setStyleSheet(""); returns it to the expected behavior.)

#include <QtWidgets>
#include <QtCore>
#include <QtGui>

int main(int argc, char *argv[]) {
	auto app = new QApplication(argc, argv);
	app->setStyleSheet("* {}");

	auto view = new QGraphicsView();
	auto scene = new QGraphicsScene(view);
	view->setScene(scene);
	view->showMaximized();

	auto proxy = new QGraphicsProxyWidget();
	auto combo = new QComboBox();
	combo->addItems({ "A", "B", "C" });
	proxy->setWidget(combo);

	scene->addItem(proxy);

	return app->exec();
}

[Axel Spoerl]

Thanks for the comprehensive report.
You have found a bug, unfortunately. I have created a ticket for it: https://bugreports.qt.io/browse/QTBUG-135340.

[Pekoyo]

Thank you very much.