如何检测对象来自什么类？ t

Question

I'm programming a physicssimulation in QT with balls and this is the collision detection I'm using to detect collision between balls.

bool Ball:: circCollide(QList <QGraphicsItem *> items) {
    QPointF c1 = mapToScene( this->boundingRect().center());
//    qDebug() << "c1x" << c1.x();
//    qDebug() << "c1y" << c1.y();
//    qDebug() << "Listcount3: " << scene()->collidingItems(this).count();

    foreach (QGraphicsItem * t, items) {
//      qDebug() << "Classname: " << typeid(t).name();
//        if (typeid(t).name() == "Ball")
        if ( t->boundingRect().width()<200)
        {
            double distance = QLineF(c1,mapToScene( t->boundingRect().center())).length();
    //        qDebug() << "tx" << mapToScene(t->boundingRect().center()).x();
    //        qDebug() << "ty" << mapToScene (t->boundingRect().center()).y();
            double radius1 = this->boundingRect().width() / 2;
            double radius2 = t->boundingRect().width() / 2;
            double radii = radius1 + radius2;
    //        qDebug () << "distance radius1: " << radius1;
    //        qDebug () << "distance radius2: " << radius2;
    //        qDebug () << "distance :" << distance;
            if ( distance <= radii )
            {
            //    qDebug() << "true collision";
                return true;
            }
        }
    }
 //   qDebug() << "false collision";
    return false;
}

Now I have the problem that this sometimes is also called for when they collide with my walls. The balls have the Class Ball which I made myself and inherits from QGraphicsItem, while the walls have the class QLineF which also inherits from Qgraphicsitem. Is there any good way to figure out whether an object "t" belongs to the class Ball? I've already tried

typeid(t).name() 

but that returns the same for both classes (P13QGraphicsItem).

Also the list I feed to at the beginning contains all objects colliding with this item hence I have to feed it a list of QGraphicsItems.

Answer 1

Override QGraphicsItem::type in Ball. Return something above the value of UserType and then call type on each QGraphicsItem to determine if it is a Ball .

Answer 2

You can try casting similar to this example:

Tag* tag = new Tag();
Polygon* polygon = new Polygon();
Polygon* polygon_cast = dynamic_cast<Polygon*>(polygon);
if(polygon_cast) qDebug() << "Cool!";
else qDebug() << "oh..";
Tag* tag_cast = dynamic_cast<Tag*>(tag);
if(tag_cast) qDebug() << "Cool!";
else qDebug() << "oh..";

Answer 3

如果Ball是从QObject派生的，并且在其声明中具有Q_OBJECT宏，则可以简单地调用QObject::metaObject和QMetaObject::className ：

t->metaObject()->className();