Returning list of objects to QML

[krobinson]

I have a QList of custom QObjects that I need to return to QML to be displayed in a ListView.

Q_PROPERTY(QList<MyObject*> myObjects READ getMyObjects)

QList<MyObject*> myObjects;

QList<MyObject*> MyClass::getMyObjects()
{
    return myObjects;
}

If I do it like this it seems to be returning a QVariant(QList<MyObject*>) to QML.

Q_PROPERTY(QList<QObject*> myObjects READ getMyObjects)

QList<MyObject*> myObjects;

QList<QObject*> MyClass::getMyObjects()
{
    QList<QObject*> objects;

    foreach(MyObject* object, myObjects)
        objects.append((QObject*)object);

    return objects;
}

If I do it this way it works fine. Is there a better way to do it without having to make a new QObject list?

[sierdzio]

You can use a model (inherit from QAbstractItemModel or something similar).

Does QVariant<QList<>> cause you any trouble on QML side? I think it might work better if you returned QVariantList, but not sure.

[J.Hilk]

hi @krobinson

you could simplyfy that a bit, but not by much:

Q_PROPERTY(QVariant myObjects READ getMyObjects)

QVariant MyClass::getMyObjects()
{
    return QVariant::fromValue(myObjects);
}

I'm not sure if myObjects has to be of QList<QObject*> or not, but I usually store my MyObject* in a QObject list and use qobject_cast<MyObject*>(myObjects.at(xyz)); should I need to modify it in c++.

[krobinson]

Up until this point I have been just storing things in a QList<QObject*> and casting in C++. It works fine that way, I just like having it declared as the actual type. It seems more clear what is going when someone comes back and looks at it. The issue I was having with the QVariant<QList<>> is that if I set a ListViews model to it, it would not work.

I had an idea that seems to work pretty well. If it has to go as a QList<QObject*> i figured I could write a template function to do it for me.

template<class T> static QList<QObject *> toQObjectList(QList<T> &list)
{
    QList<QObject*> qList;

    foreach(T item, list)
        qList.append(item);

    return qList;
}

Then I can just return it to QML like this

return Qml::toQObjectList(remoteDevices);

Seems to be a pretty good solution

[sierdzio]

Looks good indeed. I'd recommend using const QList<T> &list, though, to prevent the container from (potentially) detaching, especially if you migrate to ranged for loop at some point in the future.

[krobinson]

@sierdzio said in Returning list of objects to QML:

Looks good indeed. I'd recommend using const QList<T> &list, though, to prevent the container from (potentially) detaching, especially if you migrate to ranged for loop at some point in the future.

Good call, I will do that. Thanks.