[Qt-qml] How to trigger a QML redraw from C++

[Tarantism]

I'm writing a hybrid c++/qml application. I'm creating new items by
creating QDeclarativeItem derivatives (over-riding their paint() method)
and using their setParent method to put them in the 'scene'.

They appear properly on creation but I need to update their rendering
regularly based on c++ events.

How do I tell the QML engine to redraw these items? I've tried calling
update() on the items and their parents with no effect.