void QWidget::grabKeyboard ()
Grabs the keyboard input.
This widget receives all keyboard events until releaseKeyboard() is called; other widgets get no keyboard events at all. Mouse events are not affected. Use grabMouse() if you want to grab that.
The focus widget is not affected, except that it doesn't receive any keyboard events. setFocus() moves the focus as usual, but the new focus widget receives keyboard events only after releaseKeyboard() is called.
If a different widget is currently grabbing keyboard input, that widget's grab is released first.
根据它的描述,我想应该是要重启的。。。。
不过我最奇怪的是,为什么grabKeyboard是QWidget的成员,而却不是QPushButton的成员呢?他们之间是有继承关系的。。。。