How to resize a QGraphicsScene to a QGraphicsView?

[CassioTC]

Hi,

I'm having some trouble to resize the scene to the view size.

Here is the code:

bakgroundview.h

#ifndef BACKGROUNDVIEW_H
#define BACKGROUNDVIEW_H
 
#include <QObject>
#include <QGraphicsView>
#include <QGraphicsScene>
 
class BackgroundView : public QGraphicsView
{
    Q_OBJECT
public:
    BackgroundView(QGraphicsView *parent=0);
    ~BackgroundView() {};
 
signals:
 
public slots:
 
private:
    QGraphicsView *view;
    QGraphicsScene *scene;
 
protected:
    void resizeEvent(QResizeEvent *event);
};
 
#endif // BACKGROUNDVIEW_H

#ifndef BACKGROUNDVIEW_H
#define BACKGROUNDVIEW_H

#include <QObject>
#include <QGraphicsView>
#include <QGraphicsScene>

class BackgroundView : public QGraphicsView
{
    Q_OBJECT
public:
    BackgroundView(QGraphicsView *parent=0);
    ~BackgroundView() {};

signals:

public slots:

private:
    QGraphicsView *view;
    QGraphicsScene *scene;

protected:
    void resizeEvent(QResizeEvent *event);
};

#endif // BACKGROUNDVIEW_H

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bakgroundview.cpp

#include <QGraphicsLineItem>
#include <QResizeEvent>
 
#include "backgroundview.h"
 
BackgroundView::BackgroundView(QGraphicsView *parent)
    : QGraphicsView(parent)
{
    QGraphicsView *view = new QGraphicsView();
    QGraphicsScene *scene = new QGraphicsScene();
 
    scene->setSceneRect(0,0,view->width(),view->height());
 
    QGraphicsLineItem* line = new QGraphicsLineItem ( 0,0, scene->width(), 0 );
    QGraphicsLineItem* line2 = new QGraphicsLineItem ( scene->width(), 0 , scene->width(), scene->height() );
    QGraphicsLineItem* line3 = new QGraphicsLineItem ( scene->width(), scene->height(), 0, scene->height() );
    QGraphicsLineItem* line4 = new QGraphicsLineItem ( 0, 0, 0, scene->height() );
 
    scene->addItem(line);
    scene->addItem(line2);
    scene->addItem(line3);
    scene->addItem(line4);
 
    setScene(scene);
}
 
void BackgroundView::resizeEvent(QResizeEvent *event)
{
    //scene->setSceneRect(0, 0, event->size().width(), event->size().height());
    QGraphicsView::resizeEvent(event);
}

#include <QGraphicsLineItem>
#include <QResizeEvent>

#include "backgroundview.h"

BackgroundView::BackgroundView(QGraphicsView *parent)
    : QGraphicsView(parent)
{
    QGraphicsView *view = new QGraphicsView();
    QGraphicsScene *scene = new QGraphicsScene();

    scene->setSceneRect(0,0,view->width(),view->height());

    QGraphicsLineItem* line = new QGraphicsLineItem ( 0,0, scene->width(), 0 );
    QGraphicsLineItem* line2 = new QGraphicsLineItem ( scene->width(), 0 , scene->width(), scene->height() );
    QGraphicsLineItem* line3 = new QGraphicsLineItem ( scene->width(), scene->height(), 0, scene->height() );
    QGraphicsLineItem* line4 = new QGraphicsLineItem ( 0, 0, 0, scene->height() );

    scene->addItem(line);
    scene->addItem(line2);
    scene->addItem(line3);
    scene->addItem(line4);

    setScene(scene);
}

void BackgroundView::resizeEvent(QResizeEvent *event)
{
    //scene->setSceneRect(0, 0, event->size().width(), event->size().height());
    QGraphicsView::resizeEvent(event);
}

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main.cpp

#include <QApplication>
#include "backgroundview.h"
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
 
    BackgroundView BgView;
    BgView.showMaximized();
 
    return app.exec();
}

#include <QApplication>
#include "backgroundview.h"

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


    BackgroundView BgView;
    BgView.showMaximized();

    return app.exec();
}

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When I remove the comment from the scene resize line, the window just close realy fast with an error.

How can I resize the scene to view every time the view was resized?

Thanks

[qlands]

Hi,

You have an error in your code:

You have declared the private members in the .h:

QGraphicsView *view;
QGraphicsScene *scene;

But then in the constructor you re-declare them as local:
QGraphicsView *view = new QGraphicsView();
QGraphicsScene *scene = new QGraphicsScene();

Here you did not initialize the private member scene so because you use it in resizeEvent. it crash.

To fix it:

You need to change those lines to:
view = new QGraphicsView(); //Initialize the private member view
scene = new QGraphicsScene(); //Initialize the private member scene

Here because you already initialize scene resizeEvent will not crash.

Carlos

[wysota]

Why do you want to change the scene size when the view resizes? Maybe you want to zoom the scene instead of changing its coordinate range? Because I don't see any reasonable explanation why someone would want to do that.