No redraw of QML view in 64bit Win7 (update() in QDeclarativeItem is ignored)

I work on a QML-based UI where some elements are implemented in C++ plugin. Everything worked fine so far in WinXP 32bit and Win7 32bit. Last week I got new laptop with Win7 64bi开发者_如何学Pythont on board, and my code does not work properly there. Several seconds after start-up application behaves nicely, but then suddenly view stops redrawing. Neither QML-initiated events, nor plug-in calls to QDeclarativeItem::update() work. In plugin I am 100% sure that update() is called, but then I know, that calls to overriden QGraphicsItem::paint() do not happen as expected. The view only gets redrawn when window gets/looses focus.

I have quickly verified my application on a desktop running Win7 and had no problems there. This leads my to suspect that there is something different about how Windows 7 requests window update on my laptop and on other computers, however I am unable to figure out the difference right now.

Can someone help me out to understand what is going on there?

Thanks in advance!

p.s. Unfortunately my primitive mock-ups did not exhibit same problem, and I cannot share production code. If I will find a way to reproduce this problem in a prototype before actual solution will be found, I will post it.

Add a qapp->processEvents() after your update() call, it will probably work.
(I've come across a similar problem, but it happens on all platforms, hopefully this solution will work for you)

The answer to my question lays in something I overlooked initially in my problem description. The QDeclarativeItem::update() function was called from a non-Qt thread (certainly not GUI thread). I re-routed the call through Qt event loop and the problem was gone.

I was on Qt 4.7/4.8 at that time and cannot say how it'd behave in Qt 5.x.