如果用setVisible(false)会有一部分空缺,怎么解决?
graphicsView->setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
http://zhidao.baidu.com/question/262551045326403165
http://www.qtcn.org/bbs/simple/?t52827.html
horizontalScrollBar()->setVisible(bool visible);