QVariant: unknown user type

[sp3x]

Hello,

I want to store data by QSettings. Converting and storing the data with QSettings is possible. But if I want to load the data from QSettings I get the error:

"QVariant::load: unknown user type with name HostList."

I've already seen, that I have to register the type with Q_DECLARE_METATYPE.
But it's still not working.

That's my code to load the data with QSettings:

void MainForm::loadSettings()
{
    QSettings settings;
    QVariant hosts = settings.value("hosts");

    tblHosts->setHosts(hosts.value<HostsTableWidget::HostList>()); //  Thats where the error occures
}

And thats the class where the types are defined:

namespace Widget {

class HostsTableWidget : public QTableWidget
{
    Q_OBJECT

public:

    typedef QPair<QString, quint16> Host;
    typedef QList<Host> HostList;

    HostsTableWidget(QWidget *parent = nullptr);

    void addHost(QString hostname = "example.com", quint16 port = 80);
    void removeCurrentHost();

    HostList hosts();
    void setHosts(HostList hosts);

signals:
    void hostsChanged();
};

} // namespace Widget

Q_DECLARE_METATYPE(Widget::HostsTableWidget::Host)
Q_DECLARE_METATYPE(Widget::HostsTableWidget::HostList)

Thank you!

[sp3x]

@Christian-Ehrlicher said in QVariant: unknown user type:

qRegisterMetaType
Thank you very much. That's working. I've already played around with qRegisterMetaType but I missed to pass the right argument to the function ("Widget::HostsTableWidget::HostList")

[JonB]

@sp3x
What version of Qt are you using, is it Qt 6.x? Recently @Christian-Ehrlicher fielded a similar question and found a bug/regression in Qt 6.x handling of enums with QSettings which I think was just like this. I will try to locate it.... Ah, see https://forum.qt.io/topic/142601/wrong-enum-value-from-qsettings-using-qt- and https://bugreports.qt.io/browse/QTBUG-109744. Is this your issue too? There is an accepted solution/workaround in that thread.

[sp3x]

@JonB Hi, thank you. Sorry, yes of course I'am using Qt6.4.2. I will take a look at it an reply later.

//EDIT: No i think it's not the same issue :(

[Christian Ehrlicher]

Q_DECLARE_METATYPE(Widget::HostsTableWidget::Host)

hosts.valueHostsTableWidget::HostList()

I would try the correct full namespace here.

[sp3x]

@Christian-Ehrlicher Thank you. I've already tried it with the full namespace, but without success.

[Christian Ehrlicher]

This works fine for me without any errors with Qt6.6, looks like qRegisterMetaType<>() is needed even though I get the correct values (but a runtime warning).

namespace Widget {
    class HostsTableWidget {
    public:
        typedef QPair<QString, quint16> Host;
        typedef QList<Host> HostList;
    };
}
Q_DECLARE_METATYPE(Widget::HostsTableWidget::Host)
Q_DECLARE_METATYPE(Widget::HostsTableWidget::HostList)

int main(int argc, char* argv[])
{
    QCoreApplication a(argc, argv);
    qRegisterMetaType<Widget::HostsTableWidget::HostList>("Widget::HostsTableWidget::HostList");

    Widget::HostsTableWidget::Host h1{ "host1", 4711 };
    Widget::HostsTableWidget::Host h2{ "host2", 4712 };
    Widget::HostsTableWidget::HostList hlIn = { h1, h2 };
    QSettings s("D:\\temp.ini", QSettings::IniFormat);
    QVariant v = QVariant::fromValue(hlIn);
    auto hlOut1 = v.value<Widget::HostsTableWidget::HostList>();
    s.setValue("hostlist", v);
    s.sync();
    v = s.value("hostlist");
    auto hlOut2 = v.value<Widget::HostsTableWidget::HostList>();
    qDebug() << hlIn.size() << hlOut1.size() << hlOut2.size();
    return 0;
}

[sp3x]

@Christian-Ehrlicher said in QVariant: unknown user type:

qRegisterMetaType
Thank you very much. That's working. I've already played around with qRegisterMetaType but I missed to pass the right argument to the function ("Widget::HostsTableWidget::HostList")

[Christian Ehrlicher]

@sp3x said in QVariant: unknown user type:

@Christian-Ehrlicher said in QVariant: unknown user type:

qRegisterMetaType
Thank you very much. That's working. I've already played around with qRegisterMetaType but I missed to pass the right argument to the function ("Widget::HostsTableWidget::HostList")

Yes, it should/must be the fully qualified name.