c++ - 从基方法获取派生类

Question

我有 3 个类 Entity、Character 和 Item。当我做的时候

Character * Player = new Character(QRectF(0, 0, 50, 50), "player", theScene);
Player->setVelocityX(30)->setAttackPoint(10);

编译器提示错误:'class Entity' 没有名为'setAttackPoint' 的成员。如何让 Entity* setVelocityX(qreal vx); 返回一个 Character 指针或一个 Item 指针？

.

class Entity : public QObject, public QGraphicsPolygonItem
{
    Q_OBJECT

    public:
        Entity();
        Entity(qreal x, qreal y, qreal w, qreal h, QString tag, QGraphicsScene *scene = 0, QGraphicsItem *parent = 0);
        Entity(QRectF position, QString tag, QGraphicsScene *scene = 0, QGraphicsItem *parent = 0);
        Entity(QString tag, QGraphicsScene *scene = 0, QGraphicsItem *parent = 0);
        Entity* setVelocityX(qreal vx);
        // etc
}


class Character : public Entity
{
    Q_OBJECT

    public:
        Character(qreal x, qreal y, qreal w, qreal h, QString tag, QGraphicsScene *scene = 0, QGraphicsItem *parent = 0);
        Character(QRectF position, QString tag, QGraphicsScene *scene = 0, QGraphicsItem *parent = 0);
        Character(QString tag, QGraphicsScene *scene = 0, QGraphicsItem *parent = 0);
        Character* setAttackPoint(int attackPoint);
        //etc
}


class Item : public Entity
{
    Q_OBJECT

    public:
        enum ItemType{
            Consummable,
            Special,
            Weapon
        };

        Item(QString name, qreal x, qreal y, qreal w, qreal h,  QString tag = "item", QGraphicsScene *scene = 0, Character *parent = 0);
        Item* setOwner(Character* newOwner);
        //etc
}

Answer 1

如果您完全确定类型(否则使用 dynamic_cast 并检查结果指针是否为非 nullptr):

reinterpret_cast< Character * >( Player->setVelocityX(30))->setAttackPoint(10)

此外，根据您的代码，您不能改用函数调用的顺序吗？

Player->setAttackPoint(10)->setVelocityX(30)