Werid problem of QTWebkit in QT4.8.0

[kelvenray]

Hello All,

I am a freshman in QT.
Recently I am working on a idea that to grab the information from websites and I choose qtwebkit as my web render engine and js engine.
But now I am facing a werid problem maybe something do with the rendering of the document after loading a url.
I use webpage->mainframe()->loadUrl(%any url%) and connect the loadFinished(bool) signal with my own slot(for example finishLoading).
In the finishLoading slot I tried to find a web element with code below:

@QWebElement e = page->mainFrame()->findFirstElement("#Rent_City");@

But for this same code, the behaviours are different in 4.7.4 and 4.8.0.
For 4.7.4, the application would find this web element smoothly without any problem.
But for 4.8.0, I have tried many times but the return web element still is null. I also have tried to wait for many seconds before find the web element but it didn't work.
My release is dll and the template have set to lib.
Dramatically, while I build it into a exe, everything runs OK even build with 4.8.0.
So I don't know what happen and have searched many information but not help.

Can somebody help me to trouble shooting this problem? Many thanks.