Compiling with Qt 5.14 gives: "Unable to assign QJSValue to QVector<QPointF>" , was not in Qt 5.13

plover

I was just updating the Qt version from Qt 5.13 to Qt 5.14. Everything works fine in Qt 5.13 but now after the upgrade I started to get this printout

qrc:/qml/Component.qml:24:9: Unable to assign QJSValue to QVector<QPointF>

And sure enough, the CustomQuickItem is no longer displayed on screen.

Example code:

Component.qml

Repeater
{
    model: _cppdatamodel
    
    CustomQuickItem
    {
      ....
        positions: model.positions   //<-Component.qml:24 where the error occurs  in Qt 5.14.0 not Qt 5.13.0
      .... 
   }
}

The data method in the DataModel

QVariant DataModel::data( const QModelIndex & index, int role ) const
{
    if( ( index.row() < 0 ) || ( index.row() > rowCount() ) )
    {
        return QVariant();
    }

    auto dataVariant = m_variantList.at( index.row() );

    switch( role )
    {
       ....
        case PositionsRole:
            return QVariant::fromValue< QVector< QPointF > >( dataVariant.positions() );
        default:
            return QVariant();
    }

}

DataVariant.h

namespace model
{
class DataVariant
{
Q_GADGET

public:
    DataVariant();

   .... 

    QVector< QPointF > positions() const;

   ... 


};
}
Q_DECLARE_METATYPE( QVector< QPointF > )

And CustomQuickItem.h

class CustomQuickItem : public QQuickItem
{
Q_OBJECT

Q_PROPERTY( QVector< QPointF > positions MEMBER m_positions );

public:

    CustomQuickItem();
    ~CustomQuickItem();

...

private:
    ...
    QVector< QPointF > m_positions;
   ...

Any ideas what has changed in Qt 5.14 that might cause this problem?

plover

I've been trying to figure out from the release notes for Qt 5.14 what might have changed to cause this issue, but with no luck. I think it is strange that this worked fine in Qt 5.13 but does not work in Qt 5.14.

By changing the QVector<QPointF> to a QVariantList fixes this issue.

Christian Ehrlicher

Provide a minimal, compilable example and create a bug report.

plover

@Christian-Ehrlicher : I created a bug report https://bugreports.qt.io/browse/QTBUG-80916 with a minimal viable example.