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Adding a high number of QML objects in a QWidget application using QQuickView or QQuickWidget poses performance problem

I'm developping a Qt application in which the user can add QML objects inside a QGraphicsScene. The available QML objects are listed and the user can add as many as he wants.

Until now, I used QQuickWidgets. The QGraphicsScene contains a top-level widget which is the parent of all the QQuickWidgets I create. It works fine, but I have a performance problem. With a high number of objects, the application starts to slow down, and takes too much space in RAM (more than 1.5 GB with the first example I created, containing 400 objects).

I thought it comes from the way QQuickWidgets are handled by Qt, and wanted to try another way, with QQuickViews. To do so I created a root view, converted in a QWidget so I can embed it in my view, which is a QWidget. Then I add a new QQuickView in the root view for each created object.

The creation of the root view, its container and the engine:

    _rootView = new QQuickWindow();
    _rootView->resize(1024, 720);
    _rootView->show();

    QWidget *container = QWidget::createWindowContainer(_rootView, this);
    container->resize(_rootView->size());
    container->setObjectName("TopLevelQmlViewWidget");
    _layout->addWidget(container);

    _engine = new QQmlEngine(_rootView);

The creation of the QQuickViews representing the objects:

    QQuickView *view = new QQuickView(_engine, _rootView);
    view->setSource(url);
    view->setResizeMode(QQuickView::SizeViewToRootObject);
    view->show();

It works, but the problem is that each QQuickView creates its own thread, which doesn't change the way I handle it but takes place in memory. I don't understand why, because I reparent them to the root view.

So my questions are the following :

1 - Is there a way to prevent the QQuickViews to create their own threads ?

2 - Is using QQuickViews, indeed, less memory-consuming than using QQuickWidgets ?

3 - If no, how can I handle adding a big number of QML objects in a QWidget view without consuming too much memory ?

Solution

  • I think using multiple QQuickViews is a bad idea. An application usually only needs one. I would take a look at QQmlComponent instead. Here is an example:

    QQmlComponent component(_engine, QUrl::fromLocalFile("MyItem.qml"));
QQuickItem *childItem = qobject_cast<QQuickItem*>(component.create());
childItem->setParentItem(_rootView);