QT運行出錯：QObject::connect: Parentheses expected以及QObject::connect: No such slot ***

我在QGraphicsScene子類中添加了item的彈出菜單，並連接Action到槽函數，結果槽函數不起作用，輸出：QObject::connect: No such slot ***

 C++ Code 

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//選中item后彈出右鍵菜單 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 ;         }     } }

 

在類中使用信號/槽時一定要加Q_OBJECT宏，signal和slots的參數要一樣

槽函數加()： connect(toTopLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerTop()));   // 正確

切記忘了()：connect(toTopLayerAction, SIGNAL(triggered()), this, SLOT(slotLayerTop));      // 錯誤