Custom QGraphicsPixmapItem doesn't display pixmap

Question

I have made a custom QGraphicsPixMap QGraphicsItem as I need to have functions that trigger when someone clicks on it! The header for this is seen below:

#ifndef NEWGPIXMAP_H
#define NEWGPIXMAP_H

#include <QObject>
#include <QGraphicsPixmapItem>
#include <QGraphicsSceneMouseEvent>

class NewGPixmap : public QObject, public QGraphicsPixmapItem
{
    Q_OBJECT
public:
    NewGPixmap();
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
//    void mouseMoveEvent(QGraphicsSceneMouseEvent *event);
//    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
};

#endif // NEWGPIXMAP_H

And the .cpp for this can be seen here:

#include "newgpixmap.h"
#include <iostream>
#include <QPointF>

NewGPixmap::NewGPixmap()
{

}

void NewGPixmap::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    QPointF pos = event->pos();
    int x = pos.x();
    int y = pos.y();

    std::cout<<x<<" "<<y<<std::endl;
}

When I try and update the pixmap in the QGraphicsScene (stored in a variable called "scene") I get no errors however the PixMap isn't displayed.

This is the code I used prior to implementing my own QGraphicsPixMap which worked fine:

void MainWindow::on_openImage_triggered()
{
    QString fileName = QFileDialog::getOpenFileName(this, tr("Choose File"));
    QImage image(fileName);
    QGraphicsPixmapItem* item = new QGraphicsPixmapItem(QPixmap::fromImage(image));
    scene->clear();
    scene->addItem(item);
}

And now that I am using my own QGraphicsPixMap implementation, this is what code I have:

void MainWindow::on_openImage_triggered()
{
    QString fileName = QFileDialog::getOpenFileName(this, tr("Choose File"));
    QImage image(fileName);
    NewGPixmap item;
    item.setPixmap(QPixmap::fromImage(image));
    scene->clear();
    scene->addItem(&item);
}

The problem is that the pixmap wont load into the QGraphicsScene.

Thanks for your help!

Answer 1

Variables are destroyed when their scope ends, in your case "NewGPixmap item;" it is a local variable so it will be deleted when finished running on_openImage_triggered. If you want the object to not depend on the life cycle of the variable then you must use a pointer like your example with QGraphicsPixmapItem:

void MainWindow::on_openImage_triggered()
{
    QString fileName = QFileDialog::getOpenFileName(this, tr("Choose File"));
    QImage image(fileName);
    NewGPixmap *item = new NewGPixmap;
    item->setPixmap(QPixmap::fromImage(image));
    scene->clear();
    scene->addItem(item);
}