Draw the frame of a QGroupBox around a QFrame (Fusion style QGroupBox bug workaround)

l3u_

Hi :-)

I've been working on the following problem for quite some time now, and I can't get it to work.

The basic problem is that there is a bug in the Fusion style that, other than with other styles (like Breeze), causes a QGroupBox without a title to have an unneeded top border. There's a quite old bug report about this: https://bugreports.qt.io/browse/QTBUG-44056 that has been closed with a patch meanwhile. The problem is that the patch does fix the border spacing, but it introduces a new spacing issue (cf. the screenshot I posted in the bug), so it's actually not fixed.

In the Gerrit review, one dev proposed to simply use a QFrame instead of a title-less QGroupBox. While I think that simply using another widget instead of fixing a bug in Qt's default style is not the right way to go, I tried that.

Problem is that there doesn't seem to be an easy way to make a QFrame look like a QGroupBox. And here we are: Is it possible to make a QFrame draw the QGroupBox frame around it and have the same backgound color? So that the QFrame simply looks like a QGroupBox without a title and without the spcing problem?

Surely, I'd rather see Fusion to be fixed, but looking at the code I have no idea how to fix the new spacing issue. I would simply patch my local installation otherwise. And maybe, it will take another couple of years until this gets fixed upstream. If ever. So I think to work around this via a QFrame would be okay – if it looks the same, both for e. g. Breeze and Fusion. Or does somebody know how to fix Fusion? That would be the best of course ;-)

I would be really glad to be able to work around this. Thanks for all help in advance!

SGaist

Hi,

Can you provide a complete minimal compilable project on the bug report ?
That will allow for easier reproduction of your issue.

l3u_

That's quite simple, just add two or more QGroupBoxes without a title in a QVBoxLayout. Here's some minimalistic example:

main.cpp:

#include <QApplication>
#include "MainWindow.h"

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
    MainWindow mainWindow;
    mainWindow.show();
    return app.exec();
}

MainWindow.h:

#include <QMainWindow>

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow();

};

MainWindow.cpp:

#include "MainWindow.h"
#include <QVBoxLayout>
#include <QGroupBox>
#include <QLabel>

MainWindow::MainWindow()
{
    QWidget *widget = new QWidget;
    setCentralWidget(widget);
    QVBoxLayout *layout = new QVBoxLayout(widget);

    QGroupBox *box1 = new QGroupBox;
    QVBoxLayout *box1Layout = new QVBoxLayout(box1);
    box1Layout->addWidget(new QLabel(QStringLiteral("text")));
    layout->addWidget(box1);

    QGroupBox *box2 = new QGroupBox;
    QVBoxLayout *box2Layout = new QVBoxLayout(box2);
    box2Layout->addWidget(new QLabel(QStringLiteral("text")));
    layout->addWidget(box2);
}

Result using Breeze:

Same program started with -style=Fusion produces the long-known border issue:

And here's the version compiled against Qt (in my test case 5.7.1) with the 5.14 patch from the bug report applied:

l3u_

@SGaist Oh, you said I should post this at the bug report. I simply added a link to this post here, is this okay?

l3u_

… but to come back to the initial question (for a workaround):

I tried to use QFrame instead of QGroupBox for the title-less boxes. The problem is that QGroupBox does not inherit QFrame, but draws it's own frame.

Using setFrameShape(QFrame::StyledPanel) gives a similar (not the same) look for the Fusion theme:

But using e. g. KDE's Breeze theme, no frame is drawn at all:

So this is not the way to go, as I need a solution/workaround that does not only work for the Fusion theme …

SGaist

@l3u_ said in Draw the frame of a QGroupBox around a QFrame:

@SGaist Oh, you said I should post this at the bug report. I simply added a link to this post here, is this okay?

Please add the project to the report. Links can break and having a test case with the bug reports make things way easier.

l3u_

@SGaist I attached the sources. Thanks for the hint!

l3u_

Okay, I found a workaround: I define a CSS border for my QGroupBoxes which imitates thre Breeze look so that the native style isn't used, along with a property for the ones without a title, and I only use it if the Fusion style is used.

main.cpp:

if (application.style()->objectName() == QLatin1String("fusion")) {
    application.setStyleSheet(QStringLiteral(R"END(
        QGroupBox {
            border: 1px solid palette(Mid);
            border-radius: 2px;
            padding-top: 1.2em;
        }
        QGroupBox[notitle=true] {
            padding-top: 0;
        }
        QGroupBox::title {
            background-color: transparent;
            subcontrol-origin: margin;
            subcontrol-position: top center;
            padding: 0.4em 0 0;
        }
        QScrollArea {
            background-color: transparent;
        }
    )END"));
}

If a QGroupBox doesn't have a title, I define the notitle property:

someBox->setProperty("notitle", true);

The result is quite nice, although this is surely more a hack; but the only code to change are the setProperty calls that are simply ignored by the styles drawing the QGroupBoxes correctly:

Well, it works ;-)