qt QGraphicsScene additem - c++

Question

http://qt-project.org/doc/qt-4.8/qgraphicsscene.html#addItem
said
If the item is already in a different scene, it will first be removed from its old scene, and then added to this scene as a
top-level.
I want to keep the item in old scene.
how can I do this?
myscene1.addItem(item);
myscene2.addItem(item);// I don't want to remove item from myscene1

Answer 1

You can make a copy of the item :
myscene1.addItem(item);
myscene2.addItem(item->clone());

Answer 2

An item cannot occupy two scenes at the same time, in the way that you cannot be in two places at the same time.
The only way to do this is to make a copy of the item and place it in the second scene.

Answer 3

What you could do is to create a new class. e.g.
class Position
{
...
QPoinfF pos;
...
}
Then you can add that class to your item.
class Item : public QGraphicsItem
{
...
public:
void setSharedPos(Position *pos)
{
sharedPosition = pos;
}
//implement the paint(...) function
//its beeing called by the scene
void paint(...)
{
//set the shared position here
setPos(sharedPos);
//paint the item
...
}
protected:
void QGraphicsItem::mouseReleaseEvent ( QGraphicsSceneMouseEvent * event )
{
//get the position from the item that could have been moved
//you could also check if the position actually changed
sharedPosition->pos = pos();
}
private
Position *sharedPostion;
...
}
You would no have to create two items and give them both the same pointer to a Position object.
Item *item1 = new Item;
Item *item2 = new Item;
Position *sharedPos = new Position;
item1->setSharedPos(sharedPos);
item2->setSharedPos(sharedPos);
myScene1->addItem(item1);
myScene2->addItem(item2);
They should no at least share their position in the scenes.
If this works then you'll have to change the Position class to fit your needs and it should be working.
I am not quite shure if setting the position in the paint() function works. But thats how I would try to synchronise the items. If it does not work then you'll have to look for another place to update the settings of the items.
Or you could give the items a Pointer to each other and let them change the positions/settings directly.
e.g.
class Item : public QGraphicsItem
{
...
void QGraphicsItem::mouseReleaseEvent ( QGraphicsSceneMouseEvent * event )
{
otherItem->setPos(pos());
}
...
void setOtherItem(Item *item)
{
otherItem = item;
}
private:
Item *otherItem;
}
Item *item1 = new Item;
Item *item2 = new Item;
item1->setOtherItem(item2);
item2->setOtherItem(item1);
myScene1->addItem(item1);
myScene2->addItem(item2);