How to access a qml ListElement from c++

Question

I have a ListModel:

ListModel {
  ListElement {
    property: "value"
  }
  ListElement {
    property: "value2"
  }
}

which I am trying to access from a c++ Qt class.

I've managed to get a reference to the listmodel:

QQmlEngine engine;
QQmlComponent component(&engine,
            QUrl("qrc:///path.qml"));
QObject *object = component.create();

Debbuging the object gives me a QQmlListModel(adress).
object -> chlidren() gives me nothing, object -> children().count() shows 0.
I tried making a QList or QTableView from the object, but with no luck.

How can I get the values of the ListElements ?

Why do you need it this way? Do you really need whole ListModel or maybe only the value of one element? — Xplatforms
– Xplatforms, Commented Nov 23, 2017 at 14:43
@Xplatforms I've got a ListModel with different ListElements - same properies, but different values. I need a cpp counterpart - for now i populate a QAbstractListModel using invokable methods, but i was wondering if this could be done in the constructor of the class. — Piotr Adam Milewski
– Piotr Adam Milewski, Commented Nov 23, 2017 at 14:48
Why do you want to send data from QML to c ++? that is not recommended, if you give us a broader context we could suggest other better solutions. — eyllanesc
– eyllanesc, Commented Nov 23, 2017 at 15:20
Facing such issue means you have an application design problem. C++ implementation of ListModel is private and should not be used. Using custom QAbstractItemModel implementation could solve the problem. — folibis
– folibis, Commented Nov 23, 2017 at 15:27
class Q_QML_PRIVATE_EXPORT QQmlListModel : public QAbstractListModel => This means you can use the QAbstractListModel-API to read out everything you need. Also to alter the content. — derM
– derM, Commented Nov 23, 2017 at 15:39

derM · Accepted Answer · 2017-11-24 12:14:15Z

4

As QQmlListModel inherits QAbstractItemModel you can use all methods provided and implemented by this class.

More specifically you will be looking for:

rowCount() to tell you how many ListItems have been added
index(int row, int column, const QModelIndex &parent = QModelIndex()) where your column will be 0 at all times.
itemData(const QModelIndex &index) to retrieve the data.

Then you can easily iterate over the model.

QQmlComponent component(&engine, "MyQmlListModel.qml");
QObject* o = component.create();
QAbstractListModel* m = qobject_cast<QAbstractListModel*>(o);

if (m != nullptr) {
    qDebug() << m->rowCount();
    qDebug() << m->data(m->index(0, 0), 0);
}
else { qDebug() << "failed!"; }

edited Nov 24, 2017 at 12:14

answered Nov 23, 2017 at 17:12

derM

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3 Comments

Piotr Adam Milewski Over a year ago

Thanks, however, how can i call these methods on the created *QObject ? I tried casting (QAbstractListModel)object, qobject_cast<QAbstractListModel>(object), or reinterpret_cast<QAbstractListModel>(object), but all i get is invalid cast errors, or abstract return types. Should I make a new class inheriting from QAbstractListModel, and cast the object on the new class ?

derM Over a year ago

Yep, you need to use qobject_cast<QAbstractListModel*>(object) instead of qobject_cast<QAbstractListModel>(object). It will be a pointer.

derM Over a year ago

For some reason, I don't know, itemData seems to fail. Retrivel via data seems to work.

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