hehe,the problem is in file of project! *.pro!
when we use qmake -project to obtain a .pro file,it can't make a correct one!
we still have to change it by hand!so,if we take a look how the examples doing then we
know it needed to add a line at the end of this file:QT += xml
when you need use xml lib,also if you need use a thread lib you must add QT += thread
