Why is the selection border of a QGraphicsWidget not visible in QGraphicsScene?

Question

I have added a widget to a graphic scene (QGraphicScene) through a QGraphicsProxyWidget. The problem is that when I select the item it's selected, but the selection border is not visible.

Here is the code:

    QDial *dial= new QDial(); // Widget 
    dial->setGeometry(3,3,100,100);// setting offset for graphicswidget and widget

    QGraphicsWidget *ParentWidget = new QGraphicsWidget();// created to move and select on scene
    ParentWidget->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable);
    Scene->addItem(ParentWidget); // adding to scene

    QGraphicsProxyWidget *proxy = new QGraphicsProxyWidget();// adding normal widget through this one
    proxy->setWidget( DialBox );
    proxy->setParentItem(ParentWidget);

Here is the output:

How could I fix this?

Answer 1

Cause

QGraphicsWidget does not paint anything (including a selection rectangle), as seen from the source code:

void QGraphicsWidget::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    Q_UNUSED(painter);
    Q_UNUSED(option);
    Q_UNUSED(widget);
}

QGraphicsRectItem, however, does (see the source code):

void QGraphicsRectItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                              QWidget *widget)
{
    ...

    if (option->state & QStyle::State_Selected)
        qt_graphicsItem_highlightSelected(this, painter, option);
}

Solution

My solution would be to use QGraphicsRectItem instead of QGraphicsWidget as a handle to select/move the dial like this:

auto *dial= new QDial();                                        // The widget
auto *handle = new QGraphicsRectItem(QRect(0, 0, 120, 120));    // Created to move and select on scene
auto *proxy = new QGraphicsProxyWidget(handle);                 // Adding the widget through the proxy

dial->setGeometry(0, 0, 100, 100);
dial->move(10, 10);

proxy->setWidget(dial);

handle->setPen(QPen(Qt::transparent));
handle->setBrush(Qt::gray);
handle->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable);

Scene->addItem(handle); // adding to scene

This code produces the following result:

Click the dark gray area around the dial widget to select/move it or the widget itself in order to interact with it.

Answer 2

I know this question is old but here is a python code for anyone looking for the same. It will draw a border whenever the widget is clicked.

   class rectangle(QtWidgets.QGraphicsProxyWidget):
        def __init__(self):
            super().__init__()
            self.container = Container()  # a class inheriting Qwidget class
            self.setWidget(self.container)
            self.setFlag(QGraphicsItem.ItemIsSelectable, True) 
    
        def paint(self, qp, opt, widget):
            qp.save()
            pen = QtGui.QPen()
            pen.setColor(Qt.transparent)
            pen.setWidth(3)
    
    
            if self.isSelected():
                pen.setColor(Qt.yellow)  # selection color of your choice
    
            qp.setBrush(Qt.transparent)
            qp.setPen(pen)
            qp.drawRect(0, 0, self.container.width(), self.container.height())  # draws rectangle around the widget
    
    
            super().paint(qp, opt, widget)
            qp.restore()
    
        def mousePressEvent(self, event):
    
            if event.button() == Qt.LeftButton:
                self.setSelected(True)
            
            super().mousePressEvent(event)