my QGraphicView problem

[irmakci]

Hi,
I used the code below normally in QApplication

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QPixmap pix;
    QGraphicsView* gr;
    //QImage image;
    QString currentFile = QFileDialog::getOpenFileName(0,"Open File", QDir::currentPath());
    QImage image(currentFile);
    QGraphicsScene scene = new QGraphicsScene();
    //pix.load(":/Resources/open.png");
    //pix.load(currentFile);
 
    scene.addPixmap(QPixmap::fromImage(image));
    gr= new QGraphicsView();
    gr->setScene(&scene);
    //setCentralWidget(gr);
    gr->show();
 
    return a.exec();
}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    QPixmap pix;
    QGraphicsView* gr;
    //QImage image;
    QString currentFile = QFileDialog::getOpenFileName(0,"Open File", QDir::currentPath());
    QImage image(currentFile);
    QGraphicsScene scene = new QGraphicsScene();
    //pix.load(":/Resources/open.png");
    //pix.load(currentFile);
    
    scene.addPixmap(QPixmap::fromImage(image));
    gr= new QGraphicsView();
    gr->setScene(&scene);
    //setCentralWidget(gr);
    gr->show();
    
    return a.exec();
}

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and this works. I can see the image loaded.

But when I used the same code in QMainWindow
such as

deneme::deneme(QWidget *parent, Qt::WFlags flags)
    : QMainWindow(parent, flags)
{
    ui.setupUi(this);
    QPixmap pix;
    QGraphicsView* gr;
    //QImage image;
    QString currentFile = QFileDialog::getOpenFileName(0,"Open File", QDir::currentPath());
    QImage image(currentFile);
    QGraphicsScene scene = new QGraphicsScene();
 
    scene.addPixmap(QPixmap::fromImage(image));
    gr= new QGraphicsView();
    //gr->setBackgroundBrush(QImage(currentFile));
    //gr->setForegroundBrush(QImage(currentFile));
    gr->setScene(&scene);
    //setCentralWidget(gr);
    gr->show();    
 
}

deneme::deneme(QWidget *parent, Qt::WFlags flags)
    : QMainWindow(parent, flags)
{
    ui.setupUi(this);
    QPixmap pix;
    QGraphicsView* gr;
    //QImage image;
    QString currentFile = QFileDialog::getOpenFileName(0,"Open File", QDir::currentPath());
    QImage image(currentFile);
    QGraphicsScene scene = new QGraphicsScene();
       
    scene.addPixmap(QPixmap::fromImage(image));
    gr= new QGraphicsView();
    //gr->setBackgroundBrush(QImage(currentFile));
    //gr->setForegroundBrush(QImage(currentFile));
    gr->setScene(&scene);
    //setCentralWidget(gr);
    gr->show();    
    
}

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this does not work. And I can only see white graphics widget when I loaded the image.

How can I solve this problem. Thanks in advance
regards