问题

I have added a widget to a graphic scene (QGraphicScene) through a QGraphicsProxyWidget. To move and select the widget added QGraphicsRectItem handle. To resize widget added QSizegrip to widget. But when i resize widget more than the QGraphicsRect item rect right and bottom edges goes behind .How to overcome this problem? When i resize widget graphics rect item should resize or vice-versa should happen. how to do this? Any other ideas are welcome. Here is the code

     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);

     QSizeGrip * sizeGrip = new QSizeGrip(dial);
     QHBoxLayout *layout = new QHBoxLayout(dial);
     layout->setContentsMargins(0, 0, 0, 0);
     layout->addWidget(sizeGrip, 0, Qt::AlignRight | Qt::AlignBottom);

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

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

Here is the Output::
Before Resize
After Resize

回答1:

Cause

The QGraphicsRectItem, which you use as a handle, is not aware of the size changes of QDial, so it does not respond by resizing itself.

Limitation

QWidget and its subclases do not provide something like a sizeChanged signal out of the box.

Solution

Considering the cause and the given limitation, my solution would be the following:

In a subcalss of QDial, say Dial, add a new signal void sizeChanged();
Reimplement the resizeEvent of Dial like this:

in dial.cpp

void Dial::resizeEvent(QResizeEvent *event)
{
    QDial::resizeEvent(event);

    sizeChanged();
}

Change auto *dial= new QDial(); to auto *dial= new Dial();
Add the following code after Scene->addItem(handle); // adding to scene:

in the place, where your example code is

connect(dial, &Dial::sizeChanged, [dial, handle](){
        handle->setRect(dial->geometry().adjusted(-10, -10, 10, 10));
    });

Note: This could be also solved using eventFilter instead of subclassing QDial. However, from your other question I know that you already subclass QDial, that is why I find the proposed solution more suitable for you.