Not able to move QGraphicsEllipseItem on the scene

[alex.agape94]

Hi guys!
I've been trying to solve this problem for a couple of days now, and I can't seem to be able to find a solution for it.
Basically I have my own QGraphicsView, with my own QGraphicsScene and my own QGraphicsEllipseItem. I want to be able to move the Ellipse in the scene.
Until now I tried using the mouse events and the itemChange functions, but with no success.
In short, I want to be able to move the points in my scene only on the y-axis. Using the mouse events I was able to move the points, but they were all over the place. With the itemChange function they don't move at all.
Any ideas?


Here is some code:

The QGraphicsEllipseItem class implementation:

PunctGrafic::PunctGrafic(int x, int y, QGraphicsItem *parent)
{
    // this->setParentItem(parent);
    QPen pen;
    pen.setBrush(QBrush(Qt::SolidPattern));
    pen.setWidth(3);
    pen.setColor(QColor(Qt::red));
    this->setPen(pen);
    this->setRect(x - 1.5 , y - 1.5 , 3 , 3);
    setFlag(QGraphicsItem::ItemIsSelectable,true);
    setFlag(QGraphicsItem::ItemIsMovable,true);
    setFlag(QGraphicsItem::ItemSendsGeometryChanges,true);
    setFlag(QGraphicsItem::ItemSendsScenePositionChanges,true);
 
}
 
QVariant PunctGrafic::itemChange(GraphicsItemChange change, const QVariant &value)
{
 
    if (change == QGraphicsItem::ItemPositionChange)
        return QPointF(pos().x(), value.toPointF().y());
    return QGraphicsItem::itemChange(change, value);
 
}

PunctGrafic::PunctGrafic(int x, int y, QGraphicsItem *parent)
{
    // this->setParentItem(parent);
    QPen pen;
    pen.setBrush(QBrush(Qt::SolidPattern));
    pen.setWidth(3);
    pen.setColor(QColor(Qt::red));
    this->setPen(pen);
    this->setRect(x - 1.5 , y - 1.5 , 3 , 3);
    setFlag(QGraphicsItem::ItemIsSelectable,true);
    setFlag(QGraphicsItem::ItemIsMovable,true);
    setFlag(QGraphicsItem::ItemSendsGeometryChanges,true);
    setFlag(QGraphicsItem::ItemSendsScenePositionChanges,true);

}

QVariant PunctGrafic::itemChange(GraphicsItemChange change, const QVariant &value)
{

    if (change == QGraphicsItem::ItemPositionChange)
        return QPointF(pos().x(), value.toPointF().y());
    return QGraphicsItem::itemChange(change, value);

}

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and here is what i tried to do with the mouse events, but to no success:

void PunctGrafic::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {
        //moveStarted = true;
        this->setCursor(QCursor(Qt::ClosedHandCursor));
        QGraphicsItem::mousePressEvent(event);
        event->accept();
        return;
    }
    event->ignore();
}
////---------------------------------------------------------------------------------------------
void PunctGrafic::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {/*
            int g =
            int h = mapToScene(event->pos()).y();*/
            this->setPos(mapToItem(parentItem(),mapToParent(event->pos()).x(),mapToParent(event->pos()).y()));
            QGraphicsItem::mouseMoveEvent(event);
 
        event->accept();
        return;
    }
    event->ignore();
}
////---------------------------------------------------------------------------------------------
void PunctGrafic::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        //moveStarted = false;
        this->setCursor(QCursor(Qt::ArrowCursor));
        QGraphicsItem::mouseReleaseEvent(event);
        event->accept();
        return;
    }
    event->ignore();
}
//---------------------------------------------------------------------------------------------

void PunctGrafic::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {
        //moveStarted = true;
        this->setCursor(QCursor(Qt::ClosedHandCursor));
        QGraphicsItem::mousePressEvent(event);
        event->accept();
        return;
    }
    event->ignore();
}
////---------------------------------------------------------------------------------------------
void PunctGrafic::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
    if(event->button() == Qt::LeftButton)
    {/*
            int g =
            int h = mapToScene(event->pos()).y();*/
            this->setPos(mapToItem(parentItem(),mapToParent(event->pos()).x(),mapToParent(event->pos()).y()));
            QGraphicsItem::mouseMoveEvent(event);

        event->accept();
        return;
    }
    event->ignore();
}
////---------------------------------------------------------------------------------------------
void PunctGrafic::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
{
    if (event->button() == Qt::LeftButton)
    {
        //moveStarted = false;
        this->setCursor(QCursor(Qt::ArrowCursor));
        QGraphicsItem::mouseReleaseEvent(event);
        event->accept();
        return;
    }
    event->ignore();
}
//---------------------------------------------------------------------------------------------

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Thank you!

[Ginsengelf]

Hi, if you want to move the item only in Y direction, why do you change the X position?
this->setPos(mapToItem(parentItem(),mapToParent(event->pos()).x(),mapToParent(event->pos()).y()));

Ginsengelf

[alex.agape94]

Thank you for responding!

The issue is that they don't move at all. I was thinking that it has to be a flag or something that I forgot or something.
I simply don't understand why they refuse to move. I tried debugging, and when I click an item, the itemChange() function is being called, but it doesn't enter the if statement with change == QGraphicsItem::ItemPositionChange . In the debugging window, change = ItemClickChange or something like that, so it just sees the click, not the move event. I don't know why...

[Santosh Reddy]

No need intercept mouse events.

class EllipseItem : public QGraphicsEllipseItem
{
public:
    EllipseItem(const QRectF & rect, QGraphicsEllipseItem * parent = nullptr)
        : QGraphicsEllipseItem(rect, parent)
    {
        setFlags(ItemIsMovable | ItemSendsGeometryChanges);
    }
 
protected:
    QVariant itemChange(GraphicsItemChange change, const QVariant & value) override
    {
        if(change == ItemPositionChange)
            return QPointF(scenePos().x(), value.toPointF().y());
 
        return QGraphicsEllipseItem::itemChange(change, value);
    }
};

class EllipseItem : public QGraphicsEllipseItem
{
public:
    EllipseItem(const QRectF & rect, QGraphicsEllipseItem * parent = nullptr)
        : QGraphicsEllipseItem(rect, parent)
    {
        setFlags(ItemIsMovable | ItemSendsGeometryChanges);
    }

protected:
    QVariant itemChange(GraphicsItemChange change, const QVariant & value) override
    {
        if(change == ItemPositionChange)
            return QPointF(scenePos().x(), value.toPointF().y());

        return QGraphicsEllipseItem::itemChange(change, value);
    }
};

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