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

[faiszalkhan]

This post is deleted!

[faiszalkhan]

This post is deleted!

[faiszalkhan]

I had previously given a static bounding rect value as the previous implementation was static. Now that the value is dynamic I had not changed the contents of the bounding rect as the size has not changed from the previous implementation.

Making the changes in the bounding rect solved the problem.

Thanks a lot to @mrjj @sanojsubran @SGaist !