Serialising QList<int> with QSettings

**agarny** · 25th February 2014, 16:14

Hi,

I am trying, using QSettings, to serialise various settings, which are of type QList<int>. Now, it all works fine on Windows and OS X, but for some reasons it doesn't on Linux. Here is how I do it to load and save some of those settings. Notice that I register QList<int> as a meta-type (using qRegisterMetaTypeStreamOperators), so I believe I should be all fine and, indeed, it all works as I would expect on Windows and OS X, but not on Linux. On Linux, I get a bunch of warnings like:

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.
QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.
QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.
QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.
QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.
QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.
QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::save: unable to save type 'QList<int>' (type id: 1038).

QVariant::load: unable to load type 1038.
QVariant::load: unable to load type 1038.

Just out of curiosity, I thought I would try loading/saving my settings in a different way by using QVariantList. Thus, for loading my settings, I have something like:

Qt Code:

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void CellmlAnnotationViewWidget::loadSettings(QSettings *pSettings)
{
    // Retrieve the sizes of our editing widget and of its metadata details
    // Note: we would normally do this in CellmlAnnotationViewEditingWidget, but
    //       we have one instance of it per CellML file and we want to share
    //       some information between the different instances, so we have to do
    //       it here instead...
 
    QVariantList defaultEditingWidgetSizes = QVariantList() << 0.25*qApp->desktop()->screenGeometry().width()
                                                            << 0.75*qApp->desktop()->screenGeometry().width();
    QVariantList defaultMetadataDetailsWidgetSizes = QVariantList() << 0.25*qApp->desktop()->screenGeometry().height()
                                                                    << 0.25*qApp->desktop()->screenGeometry().height()
                                                                    << 0.50*qApp->desktop()->screenGeometry().height();
 
    QVariantList editingWidgetSizes = pSettings->value(SettingsCellmlAnnotationViewEditingWidgetSizes, defaultEditingWidgetSizes).toList();
    QVariantList metadataDetailsWidgetSizes = pSettings->value(SettingsCellmlAnnotationViewMetadataDetailsWidgetSizes, defaultMetadataDetailsWidgetSizes).toList();
 
    foreach (const QVariant &editingWidgetSize, editingWidgetSizes)
        mEditingWidgetSizes << editingWidgetSize.toInt();
 
    foreach (const QVariant &metadataDetailsWidgetSize, metadataDetailsWidgetSizes)
        mMetadataDetailsWidgetSizes << metadataDetailsWidgetSize.toInt();
}

void CellmlAnnotationViewWidget::loadSettings(QSettings *pSettings)
{
    // Retrieve the sizes of our editing widget and of its metadata details
    // Note: we would normally do this in CellmlAnnotationViewEditingWidget, but
    //       we have one instance of it per CellML file and we want to share
    //       some information between the different instances, so we have to do
    //       it here instead...

    QVariantList defaultEditingWidgetSizes = QVariantList() << 0.25*qApp->desktop()->screenGeometry().width()
                                                            << 0.75*qApp->desktop()->screenGeometry().width();
    QVariantList defaultMetadataDetailsWidgetSizes = QVariantList() << 0.25*qApp->desktop()->screenGeometry().height()
                                                                    << 0.25*qApp->desktop()->screenGeometry().height()
                                                                    << 0.50*qApp->desktop()->screenGeometry().height();

    QVariantList editingWidgetSizes = pSettings->value(SettingsCellmlAnnotationViewEditingWidgetSizes, defaultEditingWidgetSizes).toList();
    QVariantList metadataDetailsWidgetSizes = pSettings->value(SettingsCellmlAnnotationViewMetadataDetailsWidgetSizes, defaultMetadataDetailsWidgetSizes).toList();

    foreach (const QVariant &editingWidgetSize, editingWidgetSizes)
        mEditingWidgetSizes << editingWidgetSize.toInt();

    foreach (const QVariant &metadataDetailsWidgetSize, metadataDetailsWidgetSizes)
        mMetadataDetailsWidgetSizes << metadataDetailsWidgetSize.toInt();
}

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while for saving them, I have something like:

Qt Code:

Switch view

void CellmlAnnotationViewWidget::saveSettings(QSettings *pSettings) const
{
    // Keep track of the sizes of our editing widget and of its metadata details
 
    QVariantList editingWidgetSizes = QVariantList();
    QVariantList metadataDetailsWidgetSizes = QVariantList();
 
    foreach (const int &editingWidgetSize, mEditingWidgetSizes)
        editingWidgetSizes << editingWidgetSize;
 
    foreach (const int &metadataDetailsWidgetSize, mMetadataDetailsWidgetSizes)
        metadataDetailsWidgetSizes << metadataDetailsWidgetSize;
 
    pSettings->setValue(SettingsCellmlAnnotationViewEditingWidgetSizes, editingWidgetSizes);
    pSettings->setValue(SettingsCellmlAnnotationViewMetadataDetailsWidgetSizes, metadataDetailsWidgetSizes);
}

void CellmlAnnotationViewWidget::saveSettings(QSettings *pSettings) const
{
    // Keep track of the sizes of our editing widget and of its metadata details

    QVariantList editingWidgetSizes = QVariantList();
    QVariantList metadataDetailsWidgetSizes = QVariantList();

    foreach (const int &editingWidgetSize, mEditingWidgetSizes)
        editingWidgetSizes << editingWidgetSize;

    foreach (const int &metadataDetailsWidgetSize, mMetadataDetailsWidgetSizes)
        metadataDetailsWidgetSizes << metadataDetailsWidgetSize;

    pSettings->setValue(SettingsCellmlAnnotationViewEditingWidgetSizes, editingWidgetSizes);
    pSettings->setValue(SettingsCellmlAnnotationViewMetadataDetailsWidgetSizes, metadataDetailsWidgetSizes);
}

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Now, the interesting bit is that... it works on Windows, OS X and... also Linux! So, could it be that I have just come across a bug with Qt (5.2.1) on Linux?...

Whatever the case, even though using QVariantList does indeed 'fixes' my problem, I would rather use my original approach, if possible (I find 'cleaner'). This aside, I am curious as what I have done wrong, if anything, in my original approach. Anyone?

Cheers, Alan.