Incorrect/weird QLocale locale for widgets under Ubuntu/GNOME

[JonB]

Qt 6.4.2 as compiled/supplied with Ubuntu 24.04. I run under GNOME desktop/windowing system, with xcb rather than Wayland.

In a QStyledItemDelegate subclass I override QString NumberItemDelegate::displayText(const QVariant &value, const QLocale &locale) const /*override*/ so as to output a numeric column with large integers to display in my default UK locale so as to get the , separator for thousands. But I do not get commas from the const QLocale &locale passed in. Which is weird, because both my default & system locales do have it:

QString NumberItemDelegate::displayText(const QVariant &value, const QLocale &locale) const /*override*/
{
    bool ok;
    int val = value.toInt(&ok);
    if (ok)
    {
        //TEMPORARY
        // Bit odd?  My widget locale seems to have OmitGroupSeparator set, preventing 1,000s being shown with their comma
        QLocale systemLocale = QLocale::system();
        QLocale defaultLocale = QLocale();

        qDebug() << "locale parameter" << locale.toString(val) << locale.numberOptions() << locale.numberOptions().testFlag(locale parameter "9971334" QFlags(0x1) true
        qDebug() << "systemLocale" << systemLocale.toString(val) << systemLocale.numberOptions() << systemLocale.numberOptions().testFlag(QLocale::OmitGroupSeparator);
        qDebug() << "defaultLocale" << defaultLocale.toString(val) << defaultLocale.numberOptions() << defaultLocale.numberOptions().testFlag(QLocale::OmitGroupSeparator);

        return defaultLocale.toString(val);
    }
    return QStyledItemDelegate::displayText(value, locale);
}

with output:

locale parameter "9971334" QFlags(0x1) true
systemLocale "9,971,334" QFlags() false
defaultLocale "9,971,334" QFlags() false

You can see for now I am having to ignore the locale passed in, but I should be able to respect that.

ChatGPT has hallucinations about there being a QGuiApplication::locale() used for widgets, but that does not exist. I am fed up chasing its suggestions. Contrary to what it says/suggests, if I look at the locale on the widget (QTableWidget) with the delegate

    QLocale locale = ui->twFlat->locale();
    qDebug() << "widget locale" << locale.toString(123456789) << locale.numberOptions() << locale.numberOptions().testFlag(QLocale::OmitGroupSeparator);

I get widget locale "123,456,789" QFlags() false. So it not a widget setting, I only see it in displayText(). Beginning to wonder whether Qt for a table item at least chooses to pass in a locale with OmitGroupSeparator set deliberately...?

• Can anyone try this on Ubuntu/GNOME or similar to see if they get the same, please?
• Does anyone know where/how the locale being passed in here gets its settings from, such that it and only it has QLocale::OmitGroupSeparator set?
• If this is from some sort of GNOME/mutter/whatever setting, does anyone know where that is so I can look at/alter it.

[JonB]

@Christian-Ehrlicher
OK, https://codebrowser.dev/qt6/qtbase/src/widgets/itemviews/qabstractitemview.cpp.html#3947 ( QAbstractItemView::initViewItemOption())

    option->locale = locale();
    option->locale.setNumberOptions(QLocale::OmitGroupSeparator);

OK, fair enough! Thanks. I'll mark this as solution for any future readers :)

[Christian Ehrlicher]

See qabstractitemview.cpp, line 4015

[JonB]

@Christian-Ehrlicher
For me https://codebrowser.dev/qt6/qtbase/src/widgets/itemviews/qabstractitemview.cpp.html#4015 is just a comment against QAbstractItemView::scrollDirtyRegion(). Could you provide the link for whatever to look at, please?

[JonB]

@Christian-Ehrlicher
OK, https://codebrowser.dev/qt6/qtbase/src/widgets/itemviews/qabstractitemview.cpp.html#3947 ( QAbstractItemView::initViewItemOption())

    option->locale = locale();
    option->locale.setNumberOptions(QLocale::OmitGroupSeparator);

OK, fair enough! Thanks. I'll mark this as solution for any future readers :)