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Bool QGraphicsItem::contains(const QPointF &point) const is never called



  • Hi all,

    I'm using the Qt Graphics Framework for a while and now I suddenly discovered that the function metioned in the title won't get called. Here is the minimal code example (using Windows 7 and Qt 4.7.1 to Qt 4.7.4):

    @#include <QtGui>
    #include <QDebug>
    #include <QTime>

    class Item : public QGraphicsItem
    {
    public:
    inline Item()
    {
    this->setFlags(QGraphicsItem::ItemIsSelectable | QGraphicsItem::ItemIsMovable);
    }

    inline QRectF boundingRect() const
    {
        return QRectF(QPointF(0, 0), QPointF(100, 100));
    }
    inline QPainterPath shape() const
    {
        qDebug() << __FUNCTION__ << QTime::currentTime();
        QPainterPath path;
        path.addRect(this->boundingRect());
        return path;
    }
    inline bool contains(const QPointF &point) const
    {
        qDebug() << __FUNCTION__ << QTime::currentTime();
        return this->boundingRect().contains(point);
    }
    inline void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
    {
        painter->drawRect(this->boundingRect());
    }
    

    };

    int main(int argc, char *argv[])
    {
    QApplication a(argc, argv);

    QGraphicsScene scene;
    scene.addItem(new Item);
    
    QGraphicsView view(&scene);
    view.show();
    
    return a.exec(&#41;;
    

    }@

    Maybe I should let it go and use contains in the mousePressEvent? It's strange because "the doc":http://doc.qt.nokia.com/stable/qgraphicsitem.html#contains says QGraphicsView calls contains, which calls shape by default... but the only called is shape. It's like my own contains doesn't override the QGraphicsItem contains.



  • I think you misinterpreted the API docs:
    The docs gives an example when contains() is called: detecting whether the mouse curser is over a certain item.
    The docs also state, that the default implementation calls shape().

    From your above snippet I would not expect contains() to be called.



  • Yes, it looks like. I thought that mousePressEvent should call contains, which calls shape. Thanks for the quick answer!



  • Hi all,

    Just to mention that the doc is rather ambiguous on this point.
    It is explicitly stated that QGraphicsItem::contains is called from QGraphicsView to determine what item is under cursor.

    I mention this because I've noticed a very weird QGraphicsItem selection behavior in one of my apps when updating form Qt 4.6.3 to 4.8.0.
    The only description I can give, is that some items couldn't be selected, even though they clearly were under the cursor, while others were selected when not under the cursor.

    I only inherited standard Qt classes (QGraphicsRectItem, in this case), overloadeding the paint methods only, so nothing that should have an impact on selection.

    First, I was pretty surprised (until I found this thread after a few hours debugging) that QGraphicsItem::contains wasn't ever called.

    And finally though, I simply solved it by overloading QGraphicsRectItem::collidesWithPath as follows :
    @

    /**********************************************************/
    bool MyRectItem::collidesWithPath ( const QPainterPath & path, Qt::ItemSelectionMode mode ) const
    {
    return contains(path.currentPosition());
    }@

    Question is: shouldn't it be the standard behavior when it comes to finding if the item is under the cursor?



  • I would like to know if that's the intented behavior. I can't get contains called too.



  • [quote author="Skyrpex" date="1333475801"]I would like to know if that's the intented behavior. I can't get contains called too.[/quote]

    Hi Skyrpes,

    I think you misinterpreted the API docs. You should call it by yourself if you need it to be called.

    Debao


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