Best way to handle ...

Walux

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 ;)

SGaist

Hi,

It should rather be:

A * aItem = dynamic_cast(colItems.at(i));
if (aItem) {
    aItem->doSmth();
}

Walux

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 ?

SGaist

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.