Items in QGraphicsScene are not movable

faiszalkhan

Hi, I am inheriting QGraphicsScene for the class Canvas as follows,

'class Canvas : public QGraphicsScene'

This is how I'm instantiating object of Canvas in the constructor of MainWindow

scene = new Canvas(this);
ui->graphicsView->setScene(scene);

In the constructor, I am not not doing anything.

This is how I am adding object to the scene.

ellipse = scene->addEllipse(100,100,100,100,blackpen,bluebrush);
ellipse->setFlags(QGraphicsItem::ItemIsMovable);
rect = scene->addRect(-10,50,100,100,blackpen,redbrush);
rect->setFlags(QGraphicsItem::ItemIsMovable);

My observation is that the items I have added are not movable instead of setting the flag as above seen.

Previously when I had not inherited QGraphicsScene but only made an object of QGraphicsScene, the above two items were movable in the scene.

Is there something I am missing out on.
Please Help!
Thanks!

sanojsubran

Try adding the following statement also,
ellipse->setAcceptHoverEvents( true );

faiszalkhan

Tried ellipse->setAcceptHoverEvents( true );

Doesn't work.

sanojsubran

Hi,

ellipse = scene->addEllipse(100,100,100,100,blackpen,bluebrush);
ellipse->setFlags(QGraphicsItem::ItemIsMovable);
rect = scene->addRect(-10,50,100,100,blackpen,redbrush);
rect->setFlags(QGraphicsItem::ItemIsMovable);

I added these items to a custom graphics scene and the move operation works perfectly for me.

Could you please share more info/code ?
Also are you overriding the mouse events for the graphics scene class?

Regards,
San

faiszalkhan

Hi, Yes I am overriding the mousePressEvent as follows. Whereas the constructor is empty.

void Canvas::mousePressEvent(QGraphicsSceneMouseEvent *gevent)
{

/* Get the position of the mouse clicked */
QPointF pressedPosition(gevent->scenePos());

#ifdef DEBUG
qDebug("Mouse has been pressed");

  qreal temp_x = gevent->scenePos().x();
  qDebug("The value of the Xcordinate for the mouse clicked is");
  qDebug()<<temp_x;

  qreal temp_y = gevent->scenePos().y();
  qDebug("The value of the Ycordinate for the mouse clicked is");
  qDebug()<<temp_y;

#endif

/* Create the state here */
srstate = new StateItem(pressedPosition);
mainWindowPtr->scene->addItem(srstate);
srstate->setFlags(QGraphicsItem::ItemIsMovable);

}

Thanks!

sanojsubran

Try adding the statement QGraphicsScene::mousePressEvent( event ); before the end of the function

faiszalkhan

@sanojsubran I tried that but it results in a compilation error.

mrjj

@faiszalkhan
Hi
Can you list that error ?
Since its the base class that do the actual moving,
its critical to call it so lets find out what was wrong ?

faiszalkhan

@mrjj @sanojsubran It was my bad. The solution worked. However I'm not very sure as to what we did there :(

faiszalkhan

The problem is not completely solved. StateItem is a custom graphics item which inherits QGraphicsItem.
The constructor of StateItem is as shown below,

StateItem::StateItem(QPointF pos)
{
/* Get the position from the caller */
drawPos = new QPointF(pos.x(), pos.y());

//TODO: Set item as movable
setFlags(QGraphicsItem::ItemIsMovable);

}

This graphics Item is displayed on the scene but still is not movable.

Please help!
Thanks!

SGaist

Hi,

Your original problem was that by not calling the base class method implementation, you don't get the behaviour from the base class.

faiszalkhan

Since I am inheriting the QGraphicsItem in StateItem to create custom shape. Am I missing out something for setFlags(QGraphicsItem::ItemIsMovable); in the constructor to not work ?

Thanks

mrjj

Hi
You might need
setFlag(QGraphicsItem::ItemIsMovable);
setFlag(QGraphicsItem::ItemIsSelectable);

If we look at
http://doc.qt.io/qt-5/qtwidgets-graphicsview-diagramscene-example.html

It all it does to flag the items.

faiszalkhan

@mrjj said in Items in QGraphicsScene are not movable:

setFlag(QGraphicsItem::ItemIsMovable);
setFlag(QGraphicsItem::ItemIsSelectable);

Hi @mrjj , tried the same but still not working.

mrjj

Ok. cant tell what is wrong then.
You might have overridden a virtual and forgot to call base class.

Have a look at the diagram sample and see if can spot anything you
did different.

Or try the StateItem in a default scene/view.

faiszalkhan

@mrjj I just have the constructor, paint function and bounding rect. The file is as follows,

StateItem::StateItem(QPointF pos)
{

/* Get the position from the caller */
drawPos = new QPointF(pos.x(), pos.y());

//TODO: Set item as movable

// setFlags(QGraphicsItem::ItemIsFocusable);
// setFlags(QGraphicsItem::ItemIsSelectable);
setFlags(QGraphicsItem::ItemIsMovable);

// QGraphicsItem::QGraphicsItem();
}

QRectF StateItem::boundingRect() const
{
//TODO: Return a rectangle of calculated size
qreal penWidth = 1;
return QRectF(-10 - penWidth / 2, -10 - penWidth / 2,
20 + penWidth, 20 + penWidth);

}

/* Explicit call to this function is not required */
void StateItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget widget)
{
/ Set the pen */
QPen blackpen(Qt::black);
blackpen.setWidth(2);
painter->setPen(blackpen);

/* Set colour of the state */
QColor statecolor(229,231,233);
QBrush statebrush(statecolor);
painter->setBrush(statebrush);

/* Draw state item */
painter->drawRoundedRect(drawPos->x(),drawPos->y(),100,50,8,8); //x,y,width,height,xradius,yradius

QPoint p(drawPos->x(),(drawPos->y() + 10));
QPoint q((drawPos->x() + 100), (drawPos->y() + 10));
QLine stateLine(p,q);
painter->drawLine(stateLine);

// QGraphicsItem::paint(painter,option,widget);

}

mrjj

Hi
Dont it need to be selectable to be moveable ?
It all seems fine
try use the DiagramTextItem from the diagram sample (its available directly in Creator)

If that cant move, it means its your view or scene.

//! [0]
DiagramTextItem::DiagramTextItem(QGraphicsItem *parent)
    : QGraphicsTextItem(parent)
{
    setFlag(QGraphicsItem::ItemIsMovable); // BOTH 
    setFlag(QGraphicsItem::ItemIsSelectable);
}
//! [0]

//! [1]
QVariant DiagramTextItem::itemChange(GraphicsItemChange change,
                     const QVariant &value)
{
    if (change == QGraphicsItem::ItemSelectedHasChanged)
        emit selectedChange(this);
    return value;
}
//! [1]

//! [2]
void DiagramTextItem::focusOutEvent(QFocusEvent *event)
{
    setTextInteractionFlags(Qt::NoTextInteraction);
    emit lostFocus(this);
    QGraphicsTextItem::focusOutEvent(event);
}
//! [2]

//! [5]
void DiagramTextItem::mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event)
{
    if (textInteractionFlags() == Qt::NoTextInteraction)
        setTextInteractionFlags(Qt::TextEditorInteraction);
    QGraphicsTextItem::mouseDoubleClickEvent(event);
}

faiszalkhan

@mrjj Dont it need to be selectable to be moveable ?

No, Only setting it as moveable also works. I have standard QGraphicsRectItem and QGraphicsEllipseItem also in the same scene which are moving. So I don't think its the view or the scene.

:'(

mrjj

@faiszalkhan
Ok, there is something i dont see then. :)
if you provide both StateItem.h and cpp
i can try run it and see.

sanojsubran

Hi,

Comment your overriden paint method for StateItem and check whether it is working.

Also please tell how you are updating the variable "drawPos".

Regards,
San