The implementation of checkColliding() looks like this:
QList<QGraphicsItem*> items = collidingItems(m_player);
for (int i = 0, total = items.count(); i < total; ++i) {
if (Coin *c = qgraphicsitem_cast<Coin*>(items.at(i)))
c->explode();
}First we call the scene's QGraphicsScene::collidingItems() function, which takes the item for which colliding items should be detected as a first argument. With the second, optional argument, you could define how the collision should be detected. The type of that argument is Qt::ItemSelectionMode, which was explained earlier. In our case, a list of all the items that collide with m_player will be returned. So we loop through that list and check whether the current item is a Coin object. This is done by trying to cast the pointer to Coin. If it is successful, we explode the coin by calling explode(). Calling the explode() function multiple times is no problem since it...