Newb: How to access C++ QAbstractListModel from child Qml item

Gordon Smith

Starting from Qt example "AbstractItemModel", then wrapping the root Qml ListView in an Item, ListView can no longer access the model, and I cannot figure out how to do it. I want to use models outside of the root Item.

Error is:

qrc:view.qml:55:1: Required property model was not initialized 
     ListView {
 
     ^ qrc:view.qml: 55

Original QML:

ListView {
    width: 200; height: 250

    required model

    delegate: Text {
        required property string type
        required property string size

        text: "Animal: " + type + ", " + size
    }
}

New QML:

Item {
    ListView {
        width: 200; height: 250
    
        required model
        ...
    }
}

main() is:

    QQuickView view;
    view.setResizeMode(QQuickView::SizeRootObjectToView);
    view.setInitialProperties({{"model", QVariant::fromValue(&model)}});
    view.setSource(QUrl("qrc:view.qml"));

Gordon Smith

@Gordon-Smith

Three changes helped in this case:

Use setContextProperty() instead of setInitialProperties()
Assign ListView model
Don't use "model" for model name.

    //view.setInitialProperties({{"model1", QVariant::fromValue(&model)}});
    view.rootContext()->setContextProperty("model1", &model);

    ListView {
    ...
        //required model
        model: model1
    ...
    }

GrecKo

@Gordon-Smith said in Newb: How to access C++ QAbstractListModel from child Qml item:

Use setContextProperty() instead of setInitialProperties()

Don't use setContextProperty for new code
use qmlRegisterSingletonInstance instead

Your problem was that you set the model property of the Item, not the child ListView.

You could have added an alias in Item : property alias model: idOfTheListView.model
Or a property in Item and reference it in the ListView: model: idOfTheItem.model

Gordon Smith

@GrecKo Thank you for your response. I found your post about qmlregistersingletoninstance.

You are right to comment, my problem is not solved. I cannot use models in my larger app.

I understand what you are saying about properties, but I am unable to get it to work.

I'm also unable to compile a Singleton at the moment, so I stay with setContextProperty() for this post.

    view.rootContext()->setContextProperty(QStringLiteral("animalModel"), &model);

I try the following (A):

Item {
    id: root
    property alias animalModel: listView.model

    ListView {
        id: listView
        delegate: Text { text: "Animal: " + type + ", " + size }
    }
}

Probably backwards-thinking on my part. There is no QML error, and the ListView is empty.

Same result with (B):

Item {
    id: root

    ListView {
        model: root.animalModel
        delegate: Text { text: "Animal: " + type + ", " + size }
    }
}

And (C):

Item {
    id: root
    property alias animalModel2: animalModel

    ListView {
        id: listView
        model: root.animalModel2
        delegate: Text { text: "Animal: " + type + ", " + size }
    }
}

Error is: Invalid alias reference. Unable to find id "animalModel"

I'm quite lost, obviously.

dgallagher219

Setting the context property will make "animalModel" implicitly available in QML. In (A), your alias root.animalModel is shadowing your context property, which is why it doesn't work. Try this:

Item {
    id: root

    ListView {
      id: listView
      model: animalModel
      delegate: Text { text: "Animal: " + type + ", " + size }
    }
}

Incidentally, I'm a huge fan of setContextProperty, as it behaves the same as the "dummydata" folder when using qmlscene.

Gordon Smith

@dgallagher219 Turns out, your suggestion still works! It's easy to get off track. Thanks.