How to change Qt's default selection behavior?

[tushu]

I am new to QGraphicsView. So for the practice purpose I was drawing some shapes like Rectangle, Ellipse, Polygon, Polyline, Text etc.
I observed here that, whenever we click on these drawn objects ( select them using mouse click )
dashed line rectangle appears around the object which indicates that, object is selected.
If I want to change that Qt's default behavior of selection, how to do that ?

I do not want dashed rectangle around circle, when it will be clicked by mouse, but that dashed should be around its circumference.

void Widget::on_ellipsePushButton_clicked()
{
    QGraphicsEllipseItem *ellipse = new QGraphicsEllipseItem();
    ellipse = scene->addEllipse(2,2,80,80);
    QPen mPen;
    mPen.setWidth(3);
    mPen.setColor(Qt::gray);

    ellipse->setPen(mPen);
    ellipse->setBrush(QBrush(Qt::blue));

    scene->addItem(ellipse);
}

Above code simply prints ellipse.
I got help to override paint method.

void Widget::paint(QPainter *painter, QStyleOptionGraphicsItem *option, QWidget *widget)
{
    auto selected = option->state & QStyle::State_Selected;
    option->state &=  ~QStyle::State_Selected;
    paint(painter, option, widget);

    if (selected) {

      qDebug()<<"Item is selected ";
      painter->setPen(Qt::DotLine);
    }
    option->state &= selected;
}

But I dont know, how to call this paint method. I am new to Qt, can anyone help me ?

[SGaist]

Hi and welcome to devnet,

That method will be called automatically but you have put it in the wrong place.

You need to subclass QGraphicsElipseItem and add the method there.

[tushu]

@SGaist Here is my full code, I changed it according to your comment but still not able to solve problem. paint() method is not getting called. I applied some logs and found that, mousePressEvent is not occuring.

ellipse.h

class ellipse : public QGraphicsItem
{
   
public:
   ellipse();
   virtual void paint (QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
   bool pressed;

protected:
   void mousePressEvent(QGraphicsSceneMouseEvent *event);
   void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
};

widget.h     

#include "ellipse.h"
QT_BEGIN_NAMESPACE
    namespace Ui { class Widget; }
    QT_END_NAMESPACE
    class Widget : public QWidget
    {
        Q_OBJECT
    public:
        Widget(QWidget *parent = nullptr);
        ~Widget();
    private:
        Ui::Widget *ui;
        QGraphicsScene *scene;
    };

ellipse.cpp

ellipse::ellipse()
{
    pressed = false;
}
 void ellipse :: paint (QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
 {
        if(pressed)
        {
            QPainterPath path;
            path.addEllipse(2,2,220,220);
            painter->save();
            painter->setBrush(Qt::NoBrush);
            painter->setPen(QPen(option->palette.windowText(), 0, Qt::DashLine));
            painter->drawPath(path);
            painter->restore();
        }
 }

 void ellipse::mousePressEvent(QGraphicsSceneMouseEvent *event)
 {
     pressed = true;
     update();
     QGraphicsItem::mousePressEvent(event);
 }

 void ellipse::mouseReleaseEvent(QGraphicsSceneMouseEvent *event)
 {
     pressed = false;
     update();
     QGraphicsItem::mouseReleaseEvent(event);
 }

widget.cpp

#include "ellipse.h"

Widget::Widget(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::Widget)
{
    ui->setupUi(this);

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

   QGraphicsEllipseItem *ellipse1 = new QGraphicsEllipseItem();
   ellipse1 = scene->addEllipse(2,2,220,220);
   ellipse1->setFlag(QGraphicsItem::ItemIsSelectable);
   scene->addItem(ellipse1);
}

Widget::~Widget()
{
    delete ui;
}

[jsulm]

@tushu said in How to change Qt's default selection behavior?:

class ellipse : public QGraphicsItem

Shouldn't you subclass QGraphicsElipseItem as @SGaist already suggested?