setting QML properties from c++ before object creation

[guini]

I'm loading a QML file from C++ using QQmlComponent::beginCreate(). I want to set some properties before calling componentComplete(). This does not work, when the property I want to set has a property binding in the qml file.

A small example:

I have the following QML Class:

import QtQuick 2.5

Item {
    id: root

    x: 50
    y: 100

    height: 300
    width: 400

    property color c1: "red"
    property color c2: c1

    Rectangle {
        id: rect1
        color: root.c1

        x: 0
        y: 0
        width: 200
        height: root.height
    }

    Rectangle {
        id: rect2
        color: root.c2

        x: 200
        y: 0
        width: 200
        height: root.height
    }
}

and load it like this

void Loader::loadElement() {
    QQmlComponent component(engine_, "qrc:/Element.qml");
    QQuickItem* topRect = engine_->rootObjects()[0]->findChild<QQuickItem*>("topRect");

    QQuickItem* element = qobject_cast<QQuickItem*>(component.beginCreate(engine_->rootContext()));

    element->setParent(topRect);
    element->setParentItem(topRect);
    element->setProperty("c1", "green");
    element->setProperty("c2", "blue");

    component.completeCreate();
    QQmlEngine::setObjectOwnership(element, QQmlEngine::JavaScriptOwnership);

    qDebug() << "done";
}

Both c1 and c2 are set to green after loading. When I set c2 to a static value (e.g property color c2: "black")in the QML File, everything works as expected. When I call setProperty() after completeCreate() it also works.
(In my code I need to set the properties before object creation, because I do some checks of the properties on object creation.)

This behaviour seems wrong to me. Is this a bug?
If it's not a bug, is there some other way to set QML properties from C++ before object creation?

(I don't have the privileges to upload my example, sorry)

[guini]

Hey,

I found a solution. When I use a QQmlProperty to set the properties everything works as expected :-)

void Loader::loadElement() {
    QQmlComponent component(engine_, "qrc:/Element.qml");
    QQuickItem* topRect = engine_->rootObjects()[0]->findChild<QQuickItem*>("topRect");

    QQuickItem* element = qobject_cast<QQuickItem*>(component.beginCreate(engine_->rootContext()));

    QQmlProperty prop1(element, "c1", engine_);
    QQmlProperty prop2(element, "c2", engine_);

    element->setParent(topRect);
    element->setParentItem(topRect);

    // element->setProperty("c1", "green");
    // element->setProperty("c2", "blue");
    
    prop1.write("green");
    prop2.write("blue");


    component.completeCreate();
    QQmlEngine::setObjectOwnership(element, QQmlEngine::JavaScriptOwnership);

    qDebug() << "done";
}