m_Menu = new QMenu();
m_Menu->addAction(ui->action22);
m_Menu->installEventFilter(this);

m_ToolButton =new QToolButton(this);
m_ToolButton->setPopupMode(QToolButton::InstantPopup);
m_ToolButton->setToolButtonStyle(Qt::ToolButtonIconOnly);
m_ToolButton->setDefaultAction(ui->action1);
m_ToolButton->setMenu(m_Menu);
m_ToolButton->installEventFilter(this);       //安装事件过滤器

bool MainWindow::eventFilter(QObject *obj, QEvent *event)
{
    if (obj == m_ToolButton)
    {
        //如果鼠标进入，弹出菜单
        if (event->type() == QEvent::HoverEnter)
        {
            m_ToolButton->showMenu(); //弹出菜单
        }
    }
    else if(obj == m_Menu)
    {
        //菜单隐藏后
        if (event->type() == QEvent::Hide)
        {
            //关键点，需要设置WA_UnderMouse为false，让按钮认为不在鼠标下，然后再发送QEvent::HoverLeave消息，才会起到恢复hover状态的作用。
            m_ToolButton->setAttribute(Qt::WA_UnderMouse, false);
            QHoverEvent hoverEvent(QEvent::HoverLeave, QPoint(10, 10), QPoint(0, 0));
            QCoreApplication::sendEvent(m_ToolButton, &hoverEvent);
        }
    }
    return QWidget::eventFilter(obj, event);
}