QT运行出错：QObject::connect: Parentheses expected以及QObject::connect: No such slot ***

我在QGraphicsScene子类中添加了item的弹出菜单，并连接Action到槽函数，结果槽函数不起作用，输出：QObject::connect: No such slot ***

 C++ Code 

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//选中item后弹出右键菜单 if (event->button() == Qt::RightButton) {     m_pItemSelected = nullptr;     foreach (QGraphicsItem *item, items(event->scenePos()))     {         if (item->type() == QGraphicsPixmapItem::Type)         {             m_pItemSelected = item;             QMenu menu;             QAction *removeAction = menu.addAction("Remove");             QAction *toTopLayerAction = menu.addAction("To Top Layer");             QAction *toBottomLayerAction = menu.addAction("To Bottom Layer");             QAction *toUpperLayerAction = menu.addAction("To Upper Layer");             QAction *toLowerLayerAction = menu.addAction("To Lower Layer");             connect(removeAction, SIGNAL(triggered()), this, SLOT(slotRemoveItem()));             connect(toTopLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerTop()));             connect(toBottomLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerBottom()));             connect(toUpperLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerUpper()));             connect(toLowerLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerLower()));             menu.exec(event->screenPos());             break;         }     } }

在类中使用信号/槽时一定要加Q_OBJECT宏，signal和slots的参数要一样

槽函数加()： connect(toTopLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerTop()));   // 正确

切记忘了()：connect(toTopLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerTop));      // 错误