QT - mousePressEvent called 3 times when double-clicking

Question

I have created a class, GraphicPoint, that inherits both QObject and QGraphicsEllipseItem.

.h file

class GraphicPoint : public QObject, public QGraphicsEllipseItem
{
    Q_OBJECT

public:
    GraphicPoint(qreal x, qreal y, qreal width, qreal height, QWidget *parent = nullptr);

signals:
    void clicked();

private:
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
};

.cpp file

GraphicPoint::GraphicPoint(qreal x, qreal y, qreal width, qreal height, QWidget *parent) :
    QObject(parent),
    QGraphicsEllipseItem(x, y, width, height, nullptr)
{
}

void GraphicPoint::mousePressEvent(QGraphicsSceneMouseEvent *event){
    event->accept();
    emit clicked();
}

In the main window, I have created a view and a scene and added the point to the scene. Quickly clicking the button twice calls the mousePressEvent 3 times, whereas doing the same a bit slower calls it just 2 times. Here is the main window constructor

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent)
{
    n = 0;
    view = new QGraphicsView(this);
    scene = new QGraphicsScene(this);
    view->setScene(scene);
    testPoint = new GraphicPoint(0, 0, 10, 10, this);
    connect(testPoint, &GraphicPoint::clicked, [this](){
        n++;
        qDebug()<<n;
    });
    scene->addItem(testPoint);
    setCentralWidget(view);
}

After 2 quick clicks, QDebug outputs 3 lines with the numbers 1, 2, 3.

What can be the reason of this happening? Is there some default doubleclick event that calls the additional mousePressEvent?

Silnik Silnik · Accepted Answer · 2014-07-11T21:47:18

The cause of your your problem was void QGraphicsItem::mouseDoubleClickEvent, which by default calls mousePressEvent(). In order to fix this issue just overload mouseDoubleClickEvent( QGraphicsSceneMouseEvent * event ) and leave it empty.

QT - mousePressEvent called 3 times when double-clicking

1 Answers