如何禁用qgraphicsitem的多项选择？

Question

I am new to Qt. It seems the default for multiple selection of qgraphicsitem is to press ctrl button. But is it possible to disable this function? Or reload this function?

Answer 1

This is controlled by the items' flags. To disable selection for a particular item, do

item->setFlag(QGraphicsItem::ItemIsSelectable, false);

If you want to completly disable selecting items for a QGraphicsScene regardless of the item flags I would recommend to connect QGraphicsScene::selectionChanged to QGraphicsScene::clearSelection .

If you want to disable multiple selection I suggest the following:

• Subclass QGraphicsScene and keep a pointer lastSelection to a QGraphicsItem around
• Create a slot connected to QGraphicsScene::selectionChanged
• Check selectedItems :
  • it's empty: nothing to do (=nothing selected)
  • contains only lastSelection : nothing to do (=selection didn't really change)
  • contains one item, not lastSelection : set lastSelection to that item (=one item selected for the first time)
  • contains two items: One must be lastSelection . Remove that one from the selection ( lastSelection->setSelected(false); ), set lastSelection to the remaining item. (=another item was selected, move selection to it)

You might need to block signals during modifying the selection inside the slot.

Answer 2

The simple way to disable multiple selection is:

1. Create your own Dirived class from QGraphicsItem .

2. Overload the protected mousePressEvent function and disable ControlModifier :

    protected: void YourOwnQGraphicsItem::mousePressEvent(QGraphicsSceneMouseEvent *mouseEvent) Q_DECL_OVERRIDE { if(mouseEvent->modifiers() & Qt::ControlModifier) { mouseEvent->ignore(); } else { QGraphicsItem::mousePressEvent(mouseEvent); //Do what you want... } }