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Best way to handle ...

  • Hi Qt Community,

    I'm just looking for the best way to handle this situation , which I'm sure that many Qt programmers have encountered (but have easily found a solution for it :b)

    In short terms , I have this class A :

    Class A : public QGraphicsItem
    // Constructors , destructor etc...
    void doSmth ();
    // Some attributes...

    And , I have a

    class B : public QGraphicsItem{//stuff}

    So in my subclassed QGraphicsScene , I want to catch the collidingItems of class B , but since it returns a list of QGraphicsItem :

    SubScene::method ()
    //bItem is one of the attributes of my subScene
    QList<QGraphicsItem*> colItems = bItem->collidingItems ();
    for (int i=0;i <colItems.size ();i++)
    If (dynamic_cast <A*>(colItems.at (i)))
          colItems.at (i)->doSmth (); //obviously impossible 

    I have tried to use ready Lists of class A , but i dont believe them to be the best and safest solution to this.

    Any ideas ? I'll be grateful ;)

  • Lifetime Qt Champion


    It should rather be:

    A * aItem = dynamic_cast(colItems.at(i));
    if (aItem) {

  • Awesome , I never knew it can work this way , however ... doesn't this trick use slightly more memory , or it only helps to build up the reference ?

  • Lifetime Qt Champion

    It's not a trick, that's how you use dynamic_cast.

    You don't create a new object. You will use a local variable that is a pointer to your object or null if colItems.at(i) is not a pointer to an A object. Local variable that will be destroyed at the end of the function.

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