QML not registering property change from C++ property

Question

I'm displaying data in a GridView from a custom QAbstractListItem subclass (implementation here ). Adding and removing items works fine, QML is notified of the changes and transitions work fine.
Now I'm trying to set a property of an Item inside the model and have QML react on it. The problem is, the onPropertyChanged inside QML is not called.

Here is the property in C++:

// item.h
Q_PROPERTY(bool pToBeDeleted READ toBeDeleted NOTIFY toBeDeletedChanged)

// item.cpp
void Item::requestDelete()
{
    toBeDeleted_m = true;
    qDebug() << "emitting";
    emit toBeDeletedChanged();
}

This is what the GridView looks like:

// main.qml
GridView {
    id: grid

    // ...

    model: empty
    delegate: customComponent {
        toBeDeleted: pToBeDeleted
    }
    ListModel {
        id: empty
    }
}

When the program starts, grid 's model is set to my itemmodel.
And this is the QML type that does not see the changes:

// customComponentForm.ui.qml
Item {
    property bool toBeDeleted: false
}

// customComponent.qml
CustomComponentForm {
    onToBeDeletedChanged: {
        console.debug("change")
    }
}

Now when I call the method from inside the model like this:

this->items.at(i++)->requestDelete();

The output shows emitting but not change .

---

I have tried to include

emit dataChanged(createIndex(i, 0), createIndex(i, 0));

which did result in onToBeDeletedChanged to be called sometimes , but that also resulted in some wonky behaviour with the error

DelegateModel::item: index out range 3 3

Answer 1

Two things went wrong here. First, because of the ++ at

this->items.at(i++)->requestDelete();

the dataChanged emit had the wrong index which resulted in wrong items being updated. Second of all,

emit dataChanged(createIndex(i, 0), createIndex(i, 0));

was missing the third argument, and since in another attempt I had tried inline defining of a Vector the wrong way, I didn't find this to be the problem right away. The right call here would have been

QVector<int> v;

v.append(Qt::UserRole + 7 + 1);
// pToBeDeleted being the 7th property, always check this with
// roleNames()[Qt::UserRole + i + 1]. It should say your property.

emit dataChanged(createIndex(i, 0), createIndex(i, 0), v);

My mistake.

But on another note, since the rolename index seems to be platform dependent and signaling the change from the model is somewhat of a dirty approach, a better solution (as suggested by Kevin Krammer ) would be to rewrite the itemmodel to only contain a single property, which is the QObject item. That way QML is notified of the changes item's properties have.