问题

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?

回答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.

来源：https://stackoverflow.com/questions/52006987/why-is-the-selection-border-of-a-qgraphicswidget-not-visible-in-qgraphicsscene

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