QtQuick: QQmlApplicationEngine failed to load component qrc:/main.qml:23 Invalid attached object assignment

Question

Given my thoughts below am I barking up the wrong tree? Or provided the information below am I misusing Qt API to get the error in the title?

I am trying to modify the sample at http://doc.qt.io/qt-5/qtquick-scenegraph-openglunderqml-example.html to work with the default QtQuick project generated with Qt Creator 3.3.0 (opensource) Based on Qt 5.4.0 (GCC 4.6.1, 64 bit).

After looking through the code the first thing that stands out to me is:

The samples main.cpp uses:

qmlRegisterType<Squircle>("OpenGLUnderQML", 1, 0, "Squircle");

QQuickView view;
view.setResizeMode(QQuickView::SizeRootObjectToView);
view.setSource(QUrl("qrc:///scenegraph/openglunderqml/main.qml"));
view.show();

With some renaming my main.cpp uses

qmlRegisterType<MainScreen>("OpenGLUnderQML", 1, 0, "MainScreen");

QQmlApplicationEngine engine;
engine.load(QUrl(QStringLiteral("qrc:/main.qml")));

I am not sure if the difference in using a QQmlApplicationEngine over a QuickView could be causing my error:

QQmlApplicationEngine failed to load component qrc:/main.qml:23
Invalid attached object assignment

Where my main.qml looks like:

import QtQuick 2.4
import QtQuick.Window 2.2
import OpenGLUnderQML 1.0
import "qmlmodel"

Window {
    id: mainWindow
    width: 800
    height: 600
    visible: true
    color: "black"
    title: "Army Calculator"
    objectName: "mainWindow"

    ListView {
        id: mainListView
        anchors.fill: parent
        objectName: "mainListView"
    }

    MainScreen {
        SequentialAnimation on DeltaT {
            NumberAnimation { to: 1; duration: 2500; easing.type: Easing.InQuad }
            NumberAnimation { to: 0; duration: 2500; easing.type: Easing.OutQuad }
            loops: Animation.Infinite
            running: true
        }
    }
}

and the sample uses:

import QtQuick 2.0
import OpenGLUnderQML 1.0

Item {

    width: 320
    height: 480

    Squircle {
        SequentialAnimation on t {
            NumberAnimation { to: 1; duration: 2500; easing.type: Easing.InQuad }
            NumberAnimation { to: 0; duration: 2500; easing.type: Easing.OutQuad }
            loops: Animation.Infinite
            running: true
        }
    }
    Rectangle {
        color: Qt.rgba(1, 1, 1, 0.7)
        radius: 10
        border.width: 1
        border.color: "white"
        anchors.fill: label
        anchors.margins: -10
    }

    Text {
        id: label
        color: "black"
        wrapMode: Text.WordWrap
        text: "The background here is a squircle rendered with raw OpenGL using the 'beforeRender()' signal in QQuickWindow. This text label and its border is rendered using QML"
        anchors.right: parent.right
        anchors.left: parent.left
        anchors.bottom: parent.bottom
        anchors.margins: 20
    }
}

---

As per request in comment below MainScreen.h is

#ifndef MAINSCREEN_H
#define MAINSCREEN_H

#include <QQuickItem>

class MainScreenRenderer;
class QQuickWindow;

class MainScreen : public QQuickItem
{
    Q_OBJECT
    Q_PROPERTY(qreal DeltaT READ getDeltaT WRITE setDeltaT NOTIFY deltaTChanged)

public:
    MainScreen();
    ~MainScreen();

    qreal getDeltaT() const;
    void setDeltaT(qreal deltaT);

signals:
    void deltaTChanged();

public slots:
    void sync();
    void cleanup();

private slots:
    void handleWindowChanged(QQuickWindow *win);

private:
    qreal m_DeltaT;
    MainScreenRenderer *m_Renderer;
};


#endif // MAINSCREEN_H

Answer 1

Property name should start with lowercase letter. You need to change DeltaT to deltaT.

MainScreen.h

Q_PROPERTY(qreal deltaT READ getDeltaT WRITE setDeltaT NOTIFY deltaTChanged)

main.qml

MainScreen {
    SequentialAnimation on deltaT {

    }
}