Using vlQt4::Qt4Widget inside a Qt Layout

i'm playing with Qt and visualization library. I've tested the code founded here and it works great but i'm not able to insert the vlQt4::Qt4Widget widget into a QHBoxLayout instance created with designer. I have to say that i'm a Qt newbie maybe it's something very simple th开发者_如何转开发at i don't undestand. Anyway starting from the example above i'm trying to insert the widget using this line

ui->horizontalLayout->addWidget(qt4_window, 1, Qt::AlignHCenter);

but i can't see anything. The other problem is this line (taken from the example above)

qt4_window->addEventListener(applet.get());

If this line is uncommented my program crash. Is there any example of application using visualization library and Qt ? where is my error ?

Thanks a lot