Returning a custom class from a model using remote objects and qml

Suli Sahne

Hi,

Instead of assigning a role for each individual value of a model item and querying the values individually, is it possible to return an custom class from a model like this?

QVariant MyModel::data(const QModelIndex& index, int role) const
{ 
    switch (role) {
    case MyModel::ItemRole: {
        return QVariant::fromValue<MyItem*>(m_items[index.row()]);
    }
    }

    return {};
}

The MyItem class derives from QObject, does all the Q_DECLARE_METATYPE, qRegisterMetaType, qRegisterMetaTypeStreamOperators stuff and the stream operator overloads also exist:

QDataStream& operator<<(QDataStream& out, const MyItem* item);
QDataStream& operator>>(QDataStream& in, MyItem* item);

I've been trying for a while but somehow it doesn't seem to work. Whenever i want to access the items from qml

GridLayout {
    ...
    Repeater {
        // Pointer to the MyModel replica of type QAbstractItemModelReplica
        model: myModelReplica
        delegate: Item {
            // _item is the name of the MyModel::ItemRole
            property var myItem: _item
            ...
        }
    }
}

the operator>>() is called with a null pointer and after that a Out of memory occures:

Out of memory  in C:\Users\qt\work\install\include\QtCore/qvector.h, line 709

VRonin

https://wiki.qt.io/How_to_Use_a_Custom_Class_in_C%2B%2B_Model_and_QML_View

Suli Sahne

@VRonin thank a lot for your help.

When using Q_GADGET instead of the Q_OBJECT macro I don't have to derive from QObject and can therefore use value semantics. So the stream operator overloads can use a reference parameter and everything works perfectly:

QDataStream& operator<<(QDataStream& out, const MyItem& item);
QDataStream& operator>>(QDataStream& in, MyItem& item);