半模对话框 QProgressDialog

http://doc.qt.io/qt-4.8/qprogressdialog.html

progressdialog 用到了qfuture

http://blog.****.net/liang19890820/article/details/51067310

QEventLoop *loop = new QEventLoop;
QTimer::singleShot(3000, loop, SLOT(quit()));
loop->exec();