Instantiating QML Dialog from c++, "cannot find any window to open popup in"

SeDi

[Qt 5.15.2, Win10, MinGW64]
I am trying to open up a Popup or a Dialog from the c++ side.
I get this error message:

boxComp.errorString():  ""
boxComp.errors(): ()
qrc:/UserInteractionBox.qml:4:1: QML UserInteractionBox: cannot find any window to open popup in.

My code does work, if I use Window {...} instead of Popup […} or Dialog{…}, but I want to use dynamic instantiation in several contexts and I need the functionality of the QQuick items.

From c++, I instantiate it this way:

void createBox(QQuickWindow* window) {
        QQmlComponent boxComp( m_engine, QUrl( "qrc:/UserInteractionBox.qml" ) );
        qDebug()<<"boxComp.errorString(): "<<boxComp.errorString();
        qDebug()<<"boxComp.errors():"<<boxComp.errors();

        boxComp.setParent(window);
        auto obj = boxComp.create(m_engine->rootContext());
}

I call this with

auto box = new UserInteractionBox(&engine,"test", "test","test");
box->createBox(m_view);

With m_view being a controller member that holds the view used to load main.qml

m_view = new QQuickView(&engine, nullptr);

This is my Dialog, UserInteractionBox.qml:

import QtQuick 2.0
import QtQuick.Controls 2.15

Dialog {
   id: userInteractionBox
    title: "some title"
    property string text: "initialText"
    Component.onCompleted: open()

}

So:
How can I provide a valid Window to open a new item in?

SeDi

Solved. The error message, speaking about a "window", is a bit misleading, as we need to set not the window itself, but the window's contentItem() as a parent.

For posterity, my working code:

        QQuickWindow *mainWindow = qobject_cast<QQuickWindow*>(m_engine->rootObjects().value(0));
        QQmlComponent boxComp( m_engine, QUrl( "qrc:/UserInteractionBox.qml" ) );
        QVariantMap initialProperties;
        initialProperties["parent"] = QVariant::fromValue(mainWindow->contentItem());
        initialProperties["title"] = m_title;
        initialProperties["text"] = m_text;
        QQmlContext *ctxt = m_view->rootContext();
        auto obj = boxComp.createWithInitialProperties(initialProperties,ctxt);
        QMetaObject::invokeMethod(obj, "open");

As for the Dialog, my starting point is simply:

import QtQuick 2.0
import QtQuick.Controls 2.15

Dialog {
    id: userInteractionBox
    property string text: ""
    
    TextArea {
        anchors.fill: parent
        text: userInteractionBox.text
    }
}