How to correctly use QGraphicsLinearLayout together with QGraphicsScene in order to position QGraphicsItems?

Question

I'm struggling with getting QGraphicsLinearLayout to work together with QGraphicsScene such that a group of QGraphicsItems are positioned in a linear fashion on the scene. I've tried using the approach below:

#include <QApplication>
#include <QBrush>
#include <QGraphicsItem>
#include <QGraphicsLayoutItem>
#include <QGraphicsLinearLayout>
#include <QGraphicsRectItem>
#include <QGraphicsScene>
#include <QGraphicsView>
#include <QGraphicsWidget>
#include <QPen>

class MyShape : public QGraphicsRectItem, public QGraphicsLayoutItem {
  public:
    MyShape(void) {
        setPen(QPen(QBrush(Qt::black), 1));
        setBrush(QBrush(Qt::green));
        setRect(0, 0, 20, 20);
    }

    virtual QSizeF sizeHint(Qt::SizeHint which,
                            const QSizeF& constraint = QSizeF()) const {
        Q_UNUSED(which);
        Q_UNUSED(constraint);
        return boundingRect().size();
    }
};

int main(int argc, char** argv) {
    QApplication app(argc, argv);

    QGraphicsScene scene;
    MyShape* shape1 = new MyShape;
    MyShape* shape2 = new MyShape;
    MyShape* shape3 = new MyShape;
    scene.addItem(shape1);
    scene.addItem(shape2);
    scene.addItem(shape3);

    QGraphicsLinearLayout* layout = new QGraphicsLinearLayout;
    layout->addItem(shape1);
    layout->addItem(shape2);
    layout->addItem(shape3);

    QGraphicsWidget* container = new QGraphicsWidget;
    container->setLayout(layout);
    scene.addItem(container);

    QGraphicsView view;
    view.setScene(&scene);
    view.show();

    return app.exec();
}

This doesn't work, as all items are still placed on top of each other, instead of next to each other (according to the layout dictated by the linear layout). What am I doing wrong?

score 3 · Accepted Answer · answered Apr 19 '12 at 15:06

Ah, I had forgotten to override the setGeometry function!

So the implementation of the MyShape class should look like this:

class MyShape : public QGraphicsRectItem, public QGraphicsLayoutItem {
  public:
    MyShape(void) {
        setPen(QPen(QBrush(Qt::black), 1));
        setBrush(QBrush(Qt::green));
        setRect(0, 0, 20, 20);
    }

    virtual QSizeF sizeHint(Qt::SizeHint which,
                            const QSizeF& constraint = QSizeF()) const {
        Q_UNUSED(which);
        Q_UNUSED(constraint);
        return boundingRect().size();
    }

    virtual void setGeometry(const QRectF& rect) {
        setPos(rect.topLeft());
    }
};

And now it works as expected. =)

Thanks, this helped. BTW, you can accept this answer ;) – Nikita Krupenko Jun 28 '18 at 11:50 — Nikita Krupenko, Jun 28 '18 at 11:50

How to correctly use QGraphicsLinearLayout together with QGraphicsScene in order to position QGraphicsItems?

1 Answers1