Time for action – using properties, signals, and slots with items

So let's alter the Player class to use QObject:

class Player : public QObject, public QGraphicsPixmapItem {
  Q_OBJECT

All you have to do is to add QObject as a base class and add the Q_OBJECT macro. Now you can use signals and slots with items too. Be aware that QObject must be the first base class of an item.

Tip

If you want an item that inherits from QObject and QGraphicsItem, you can directly inherit QGraphicsObject. Moreover, this class defines and emits some useful signals such as xChanged() when the x coordinate of the item has changed or scaleChanged() when the item is scaled.

Note

A word of warning: Only use QObject with items if you really need its capabilities. QObject adds a lot of overhead to the item, which will have a noticeable impact on performance when you have many items. So use it wisely and not only because you can.

Let us go back to our player item. After adding QObject, we define a property called m_jumpFactor...