How to put QWindow into QWidget's layout (Qt5)

This has been fixed in Qt 5.1. Citing [1]

To remedy this problem, Qt 5.1 introduces the function QWidget::createWindowContainer(). A function that creates a QWidget wrapper for an existing QWindow, allowing it to live inside a QWidget-based application. Using QQuickView or QOpenGLContext together with widgets is now possible.

[1] https://www.qt.io/blog/2013/02/19/introducing-qwidgetcreatewindowcontainer

Found this issue on Qt-project bugtracker.

There is some workarounds in comments.