QGraphicsItem .. Scene .. View question?

[wysota]

What do you mean that the item "doesn't get the event"?

[DirtyBrush]

In the scene it gets the event, and with the qDebug() line I see on the console output

void myScene::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "scene: dropEvent";

void myScene::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "scene: dropEvent";

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'scene: drop Event'

I have a similar debug in the item dropEvent() method.

void MyNode::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dropEvent";
    QGraphicsItem::dropEvent(event);
}

void MyNode::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dropEvent";
    QGraphicsItem::dropEvent(event);
}

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But I do not see the 'Node: dropEvent' debug, so the QGraphicsItem doesn't get the event.

[wysota]

How is the shape() of the item defined? Is there a chance some other item gets the event? What does this return when ran as part of the scene's dropEvent?

qDebug() << items(event->scenePos()).count();

qDebug() << items(event->scenePos()).count();

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[DirtyBrush]

Hi,

Thanks for the reply.

It comes back with '1', which is what I'd expect, only got one item there.

--

Have found an interesting thing though...

In the view, I have dragMoveEvent of :-

void myView::dragMoveEvent(QDragMoveEvent *event) {
 }

void myView::dragMoveEvent(QDragMoveEvent *event) {
 }

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With this the dropEvent gets to the scene. However, if I add

QGraphicsView::dragMoveEvent(event);

QGraphicsView::dragMoveEvent(event);

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to this method the dropEvent doesn't.

Also, if I dont have this function defined, it also doesn't get to the
scene.

Is this this the correct behaviour?

Usually when I redefine a method I call the base class method at
the end like 'Base:SomeMethod();'.

Thanks again, I appreciate your help,

DB

[wysota]

If you don't call the base class implementation, the scene shouldn't receive the event.

[DirtyBrush]

Hello Again!

If you don't call the base class implementation, the scene shouldn't receive the event.

OK, so there's the problem? I see the exact opposite of this.

Shall we have a quick overview of my code -

View header file

class myView : public QGraphicsView
{
public:
    myView(QWidget *parent=0);
protected:
 
    void dragEnterEvent(QDragEnterEvent *event);
    void dropEvent(QDropEvent *event);
    void dragMoveEvent(QDragMoveEvent *event);
 
};

class myView : public QGraphicsView
{
public:
    myView(QWidget *parent=0);
protected:

    void dragEnterEvent(QDragEnterEvent *event);
    void dropEvent(QDropEvent *event);
    void dragMoveEvent(QDragMoveEvent *event);

};

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view methods

myView::myView(QWidget *parent) : QGraphicsView(parent) {
//        setAcceptDrops(true);
        // Comment the line below, and drop starts working
        setScene(new QGraphicsScene(this));
}
 
void myView::dragEnterEvent(QDragEnterEvent *event) {
//        event->accept();
        qDebug() << "View: dragEnterEvent";
        QGraphicsView::dragEnterEvent(event);
}
 
void myView::dropEvent(QDropEvent *event) {
    QPointF pnt;
    QPoint pos;
    QGraphicsItem * itm;
 
    qDebug() << "View sees drop";
 
    pos = event->pos();
    pnt = this->mapToScene( event->pos() );
 
    if (itm = itemAt( pos ) )
    {
        qDebug("There is an item here");
        QGraphicsView::dropEvent(event);
        return;
    }
    else
    {
        qDebug("Blank area");
    }
    // Is there something underneath?
 
    QByteArray ba = event->mimeData()->data("foo/bar");
    QDataStream ds(&ba, QIODevice::ReadOnly);
    while (!ds.atEnd()) {
        QString name;
        QString path;
        QString monid;
        MyNode * nd;
        ds >> name >> path >> monid;
        qDebug() << name << path << monid;
 
        //
        // This view is inside the central widget which is in the mainwindow, so node
        // parent is the mainwindow so it can access the action functions.  a bit
        // untiy huh?
        //
        if (QString("Button")==name)
          nd = new MyNode( (QWidget*)(this->parent())->parent(), name, path, monid, MyNode::BUTTON);
        else
          nd = new MyNode( (QWidget*)(this->parent())->parent(), name, path, monid, MyNode::POINT);
        QGraphicsScene * sc;
        sc = this->scene();
 
        pnt = this->mapToScene( event->pos() );
        qDebug() << pnt;
        nd->setPos(pnt);
        sc->addItem(nd);
    }
}
 
void myView::dragMoveEvent(QDragMoveEvent *event) {
}

myView::myView(QWidget *parent) : QGraphicsView(parent) {
//        setAcceptDrops(true);
        // Comment the line below, and drop starts working
        setScene(new QGraphicsScene(this));
}

void myView::dragEnterEvent(QDragEnterEvent *event) {
//        event->accept();
        qDebug() << "View: dragEnterEvent";
        QGraphicsView::dragEnterEvent(event);
}

void myView::dropEvent(QDropEvent *event) {
    QPointF pnt;
    QPoint pos;
    QGraphicsItem * itm;

    qDebug() << "View sees drop";

    pos = event->pos();
    pnt = this->mapToScene( event->pos() );

    if (itm = itemAt( pos ) )
    {
        qDebug("There is an item here");
        QGraphicsView::dropEvent(event);
        return;
    }
    else
    {
        qDebug("Blank area");
    }
    // Is there something underneath?

    QByteArray ba = event->mimeData()->data("foo/bar");
    QDataStream ds(&ba, QIODevice::ReadOnly);
    while (!ds.atEnd()) {
        QString name;
        QString path;
        QString monid;
        MyNode * nd;
        ds >> name >> path >> monid;
        qDebug() << name << path << monid;

        //
        // This view is inside the central widget which is in the mainwindow, so node
        // parent is the mainwindow so it can access the action functions.  a bit
        // untiy huh?
        //
        if (QString("Button")==name)
          nd = new MyNode( (QWidget*)(this->parent())->parent(), name, path, monid, MyNode::BUTTON);
        else
          nd = new MyNode( (QWidget*)(this->parent())->parent(), name, path, monid, MyNode::POINT);
        QGraphicsScene * sc;
        sc = this->scene();

        pnt = this->mapToScene( event->pos() );
        qDebug() << pnt;
        nd->setPos(pnt);
        sc->addItem(nd);
    }
}

void myView::dragMoveEvent(QDragMoveEvent *event) {
}

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Scene header

class myScene : public QGraphicsScene
{
public:
    myScene(QObject *parent);
    void dropEvent(QGraphicsSceneDragDropEvent * event);
    void dragEnterEvent(QGraphicsSceneDragDropEvent * event);
};

class myScene : public QGraphicsScene
{
public:
    myScene(QObject *parent);
    void dropEvent(QGraphicsSceneDragDropEvent * event);
    void dragEnterEvent(QGraphicsSceneDragDropEvent * event);
};

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scene code

myScene::myScene(QObject*parent): QGraphicsScene(parent)
{
}
 
void myScene::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "scene: dropEvent";
    qDebug() << items(event->scenePos()).count();
 
    this->setFocus(Qt::NoFocusReason);
 
    QGraphicsItem *gi;
 
    gi = this->itemAt( event->scenePos() );
 
    if (gi)
    {
        qDebug() << "Scene(dropEvent); there is an item thar";
        gi->setFocus(Qt::NoFocusReason);
        gi->setSelected(true);
    }
 
    QGraphicsScene::dropEvent(event);
}
 
void myScene::dragEnterEvent(QGraphicsSceneDragDropEvent * event)
{
    event->acceptProposedAction();
        QGraphicsItem *gi;
 
    gi = this->itemAt( event->scenePos() );
 
    if (gi)
    {
        qDebug() << "Scene(dragEnterEvent); there is an item thar";
        gi->setFocus(Qt::NoFocusReason);
        gi->setSelected(true);
    }
 
    qDebug() << "scene: dragEnterEvent";
    QGraphicsScene::dragEnterEvent(event);
}

myScene::myScene(QObject*parent): QGraphicsScene(parent)
{
}

void myScene::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "scene: dropEvent";
    qDebug() << items(event->scenePos()).count();

    this->setFocus(Qt::NoFocusReason);

    QGraphicsItem *gi;

    gi = this->itemAt( event->scenePos() );

    if (gi)
    {
        qDebug() << "Scene(dropEvent); there is an item thar";
        gi->setFocus(Qt::NoFocusReason);
        gi->setSelected(true);
    }

    QGraphicsScene::dropEvent(event);
}

void myScene::dragEnterEvent(QGraphicsSceneDragDropEvent * event)
{
    event->acceptProposedAction();
        QGraphicsItem *gi;

    gi = this->itemAt( event->scenePos() );

    if (gi)
    {
        qDebug() << "Scene(dragEnterEvent); there is an item thar";
        gi->setFocus(Qt::NoFocusReason);
        gi->setSelected(true);
    }

    qDebug() << "scene: dragEnterEvent";
    QGraphicsScene::dragEnterEvent(event);
}

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And finally item header

class MyNode : public QGraphicsItem
{
public:
    int MonId;
    int ValInt;
    int DataType;
    QString endnode;
    QString path;
    QString monid;
 
    enum MimicType { LAMP, BUTTON, POINT };
    MimicType mimic;
    int EditMode;
 
 
    MyNode(QWidget * parent, QString endnode, QString path, QString monid, MimicType mt);
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem * option, QWidget *widget);
    void mousePressEvent(QGraphicsSceneMouseEvent * event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent * event);
    void dropEvent(QGraphicsSceneDragDropEvent * event);
    void dragEnterEvent(QGraphicsSceneDragDropEvent * event);
    void dragMoveEvent(QGraphicsSceneDragDropEvent * event);
    void myupdate();
    void createActions();
    QAction * myAct;
    void passDrop(QDropEvent * event);
 
private slots:
    void doMyAct();
    QWidget * parent;
};

class MyNode : public QGraphicsItem
{
public:
    int MonId;
    int ValInt;
    int DataType;
    QString endnode;
    QString path;
    QString monid;

    enum MimicType { LAMP, BUTTON, POINT };
    MimicType mimic;
    int EditMode;


    MyNode(QWidget * parent, QString endnode, QString path, QString monid, MimicType mt);
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem * option, QWidget *widget);
    void mousePressEvent(QGraphicsSceneMouseEvent * event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent * event);
    void dropEvent(QGraphicsSceneDragDropEvent * event);
    void dragEnterEvent(QGraphicsSceneDragDropEvent * event);
    void dragMoveEvent(QGraphicsSceneDragDropEvent * event);
    void myupdate();
    void createActions();
    QAction * myAct;
    void passDrop(QDropEvent * event);

private slots:
    void doMyAct();
    QWidget * parent;
};

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and the item drag methods...

void MyNode::dragEnterEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dragEnterEvent";
    //event->setAccepted(true);
    //event->accept();
    event->acceptProposedAction();
    QGraphicsItem::dragEnterEvent(event);
}
void MyNode::dragMoveEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dragMoveEvent";
    event->accept();
    QGraphicsItem::dragMoveEvent(event);
}
void MyNode::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dropEvent";
    QGraphicsItem::dropEvent(event);
}

void MyNode::dragEnterEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dragEnterEvent";
    //event->setAccepted(true);
    //event->accept();
    event->acceptProposedAction();
    QGraphicsItem::dragEnterEvent(event);
}
void MyNode::dragMoveEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dragMoveEvent";
    event->accept();
    QGraphicsItem::dragMoveEvent(event);
}
void MyNode::dropEvent(QGraphicsSceneDragDropEvent * event)
{
    qDebug() << "Node: dropEvent";
    QGraphicsItem::dropEvent(event);
}

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[wysota]

What is exactly the point of intercepting those events in both the view and the scene? Do you have more than one view on the same scene and want them to behave differently?

[DirtyBrush]

Hi again,

I'll want to capture events in the view to resize the view, zoom, pan, etc.

In the scene I want to have items, which will allow drops and also
have context menu(edit mode). Then in (run mode) the items will have
mouse click events which result in some internal processing.

(These drops configure the items with various fields in a database,
then these items change colour or text when the values in the
database change)

Eventually, more complex behaviour, linking from one item to another,
moving items around, etc.

thanks again,

DB

[wysota]

But I'm asking about drop events specifically. I don't see the point in intercepting them in both the view and the scene unless you have more than one view on the same scene. In general in 90% of the cases it is enough to intercept any events just in the scene and items themselves.

[DirtyBrush]

OK, I'll try without catching these events in the view. So now I've removed
myview and am back to using the base QGraphicsView with view->setAcceptDrops(true);

However, when I drag into the view/scene pane I get the 'no entry' cursor
and cannot drop into the view/scene.

Any ideas?

DB

[wysota]

You need to reimplement dragEnterEvent on the scene and possibly dragMoveEvent as well. The same needs to be done for item classes you want to accept drops.

[DirtyBrush]

Hi,

Yes, I have dragMoveEvent, dragEnterEvent and dropEvent defined in
the scene.

I also have setAcceptDrops(true) for the scene.

However, it still has the 'no entry' cursor when trying a drag-drop into
this view/scene.

DB