QGraphicsView::itemAt() method always return zero

Question

I have some custom QGraphicsItems in a QGraphicsView of a QGraphicsScene.
I wish to know if there is an Item in the view at given (x,y) coordinates.

To test purpose I use the following class as QGraphicsScene:

class CustomScene : public QGraphicsScene
{
protected:
    void mousePressEvent(QGraphicsSceneMouseEvent *event)
    {
        if (QGraphicsItem *item = itemAt(event->scenePos())) {
            qDebug() << "You clicked on item" << item;
        } 
        else {
            qDebug() << "You didn't click on an item.";
        }
    }
};

In my application I have:

a class "Screen::Screen(QWidget *parent): QWidget(parent){...}" with inside an instance of my class "CustomScene : public QGraphicsScene {...}" described above and an instance of class QGraphicsView.
some instances of my class "Rect : public QGraphicsRectItem {...}", added to the QGraphicsView,s that draw some rectangles after some calculations.

When I launch the application and click on the drawn rectangles, I always have "You didn't click on an item." message.

Searching here in previous posts or searching on google I didn't find the reason why my code doesn't work. What am I doing wrong?

Edit 1: boundingRect() method returns correctly. I tried to add some QGraphicsRectItem, itemAt() method returns their information correctly.

yes, boundingRect() method of my custom items returns correct information. I added this and some other new information to the post "Edit 1". — diegob, May 23 '14 at 10:09
Did you override `shape()`? this is used for hit-detection, among other things — king_nak, May 23 '14 at 10:11
No, I didn't. Overriding *shape()* method, itemAt() starts to return correctly for my custom items. Thank you! — diegob, May 23 '14 at 10:36
Please post your solution as an answer to your own question. Answers to one's own questions are encouraged, when you figure things out. — Kuba hasn't forgotten Monica, May 23 '14 at 15:48

score 0 · Accepted Answer · answered May 23 '14 at 16:35

0

The problem was that I didn't override the QPainterPath QGraphicsItem::shape () const [virtual] method.
Once done, itemAt() method started to works as expected.

answered May 23 '14 at 16:35

diegob

35
6

That shouldn't be neccessary, because the default implementation returns a `QPainterPath` of the `boundingRect()`. The problem must be somewhere else. Can you please add your implementation of `shape()` to your answer? – Martin Hennings Jun 19 '18 at 08:04

QGraphicsView::itemAt() method always return zero

1 Answers1