How to set QComboBox menu background transparent?

Roberrt

I'm trying to create a combo box with rounded borders including the pop-up menu, but when I set a border-radius, it doesn't apply to the background:

Image demonstrating the issue

While searching for a way to remove this background, I found this answer: https://stackoverflow.com/questions/27962162/rounded-qcombobox-without-square-box-behind

To reproduce:

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
{
    ui.setupUi(this);

    QComboBox* comboBox = new QComboBox(this);
    
    comboBox->setStyleSheet(R"(
        QComboBox  {
            border-radius: 8px;
            margin: 10px;
            background-color: gray;
            min-height: 32px;
        }
    
        QComboBox QAbstractItemView {
            border-radius: 8px;
            margin: 10px;
            background-color: gray;
        }
    )");
    
    comboBox->move(100, 100);
    comboBox->addItem("1");
    comboBox->addItem("2");
    
    comboBox->view()->window()->setWindowFlags( Qt::Popup | Qt::FramelessWindowHint |Qt::NoDropShadowWindowHint);
    comboBox->view()->window()->setAttribute(Qt::WA_TranslucentBackground);

}

It does remove the background, but it lets a black background visible for a short:

How can I get rid of this black background?

Here's everything I already tried that didn't work:

    if (comboBox->view()->parentWidget())
    {
        auto p = comboBox->view()->parentWidget();
        p->setWindowOpacity(0);
        p->setWindowFlags( Qt::Popup | Qt::FramelessWindowHint |Qt::NoDropShadowWindowHint);
        p->setAttribute(Qt::WA_TranslucentBackground);
        p->setHidden(true);
        p->setAutoFillBackground( false );
    }

    comboBox->setAutoFillBackground( false );
    comboBox->view()->setAutoFillBackground( false );
	comboBox->view()->viewport()->setAutoFillBackground(false);
    comboBox->view()->window()->setAutoFillBackground(false);

    //comboBox->view()->setAttribute(Qt::WA_TranslucentBackground);
    //comboBox->view()->viewport()->setAttribute(Qt::WA_TranslucentBackground);
    //comboBox->view()->window()->setAttribute(Qt::WA_TranslucentBackground);

    comboBox->view()->setWindowOpacity(0);
    comboBox->view()->viewport()->setWindowOpacity(0);
    comboBox->view()->window()->setWindowOpacity(0);

    //comboBox->view()->setHidden(true);
    //comboBox->view()->viewport()->setHidden(true);
    //comboBox->view()->window()->setHidden(true);

    QPalette palette = comboBox->view()->palette();
    palette.setColor(QPalette::Window, Qt::transparent);
    comboBox->view()->setPalette(palette);

The unique thing i didn't tried yet is using a proxy as i have no experience with it.

Does someone has any idea if twerking into proxy it could be possible to get ride of that black window that appears for a short?

Roberrt

I couldn't even find a way to get a pointer to that window, which window is that?

jsulm

@Roberrt said in How to set QComboBox menu background transparent?:

I couldn't even find a way to get a pointer to that window

What window do you mean?

Roberrt

@jsulm the black window that appears when i click in the combo box, look at the gif, she appears just for 1 sec and then disappears.

Roberrt

Does this window appear only to me?

Roberrt

Does someone know if is possible to edt the popup background with a proxy style or something like?

HunterM

If you're okay with disabling the animation part of the drop down, it will prevent the black box from appearing. You do this through QApplication::setEffectEnabled:

QApplication::setEffectEnabled(Qt::UI_AnimateCombo, false);