no compile error, error on run

**sincnarf** · 18th September 2007, 07:40

I can compile my project with no error, but a windows error (send report, end task) suddenly appears when the program executes this function.

By the way, I am trying to resize a loaded Image to the scene's size keeping the image's aspect ratio. any other suggestions would be nice.

Qt Code:

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void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
{
    QString fileName = QFileDialog::getOpenFileName(this,
                       tr("Open Image"), QDir::currentPath());
    if (!fileName.isEmpty())
    {
        QImage tempImage(fileName);
        if (tempImage.isNull())
        {
            QMessageBox::information(this, tr("Load Warning"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }
        QImage image = tempImage.convertToFormat(QImage::Format_ARGB32);
        QGraphicsScene *scene = new QGraphicsScene;
        QGraphicsScene* viewScene = graphicsView->scene();
        QPixmap pixmap = QPixmap::fromImage(image);
 
        scene->addPixmap(pixmap.scaled(QSize((int)viewScene->width(), (int)viewScene->height()), Qt::KeepAspectRatio, Qt::SmoothTransformation));
 
		qDebug() << "Width = " << viewScene->width();
		qDebug() << "Height = " << viewScene->height();
 
        graphicsView->setScene(scene);
        graphicsView->show();
    }
}

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
{
    QString fileName = QFileDialog::getOpenFileName(this,
                       tr("Open Image"), QDir::currentPath());
    if (!fileName.isEmpty())
    {
        QImage tempImage(fileName);
        if (tempImage.isNull())
        {
            QMessageBox::information(this, tr("Load Warning"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }
        QImage image = tempImage.convertToFormat(QImage::Format_ARGB32);
        QGraphicsScene *scene = new QGraphicsScene;
        QGraphicsScene* viewScene = graphicsView->scene();
        QPixmap pixmap = QPixmap::fromImage(image);

        scene->addPixmap(pixmap.scaled(QSize((int)viewScene->width(), (int)viewScene->height()), Qt::KeepAspectRatio, Qt::SmoothTransformation));

		qDebug() << "Width = " << viewScene->width();
		qDebug() << "Height = " << viewScene->height();
	
        graphicsView->setScene(scene);
        graphicsView->show();
    }
}

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**marcel** · 18th September 2007, 07:57

I don't think this works:

Qt Code:

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QGraphicsScene *scene = new QGraphicsScene;

QGraphicsScene *scene = new QGraphicsScene;

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It is unlikely to be able to add items to a scene without a view. It's view is NULL and I am sure it tries to use it somewhere.

Try setting the scene to the view immediately after creating scene.

**sincnarf** · 18th September 2007, 08:17

how do I determine if the passed graphicsView and its graphicsScene is null?

i'm looking for something like a view.isNull() method and view->scene().isNull method

**marcel** · 18th September 2007, 08:23

But I already told you. The solution is to setScene right after you create it. Nothing more.
Anyway, if you want to test the view of a scene use QGraphicsScene::views(). It returns a QList of QGraphicsView. In your case it should be empty.

**sincnarf** · 18th September 2007, 09:09

Qt Code:

Switch view

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
{
 
	if (graphicsView == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("Graphics View is NULL"));
        return;
    }
    QGraphicsScene *scene = graphicsView->scene();
    QGraphicsView *view = graphicsView;
    view->setScene(scene);
     if (scene->views().size() == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("GraphicsView's GraphicsScene is NULL"));
        return;
    }
}

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
{
	
	if (graphicsView == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("Graphics View is NULL"));
        return;
    }
    QGraphicsScene *scene = graphicsView->scene();
    QGraphicsView *view = graphicsView;
    view->setScene(scene);
     if (scene->views().size() == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("GraphicsView's GraphicsScene is NULL"));
        return;
    }
}

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and this

Qt Code:

Switch view

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
{
 
	if (graphicsView == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("Graphics View is NULL"));
        return;
    }
     if ( graphicsView->scene()->views().size() == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("GraphicsView's GraphicsScene is NULL"));
        return;
    }
}

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
{
	
	if (graphicsView == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("Graphics View is NULL"));
        return;
    }
     if ( graphicsView->scene()->views().size() == 0)
    {
        QMessageBox::warning(this, tr("Load Error"), tr("GraphicsView's GraphicsScene is NULL"));
        return;
    }
}

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causes the same windows error

**marcel** · 18th September 2007, 09:39

Qt Code:

Switch view

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
      {
          QString fileName = QFileDialog::getOpenFileName(this,
                             tr("Open Image"), QDir::currentPath());
          if (!fileName.isEmpty())
          {
              QImage tempImage(fileName);
              if (tempImage.isNull())
              {
                  QMessageBox::information(this, tr("Load Warning"),
                                           tr("Cannot load %1.").arg(fileName));
                  return;
              }
              QImage image = tempImage.convertToFormat(QImage::Format_ARGB32);
              QGraphicsScene *scene = new QGraphicsScene;
              QGraphicsScene* viewScene = graphicsView->scene();
          float w = viewScene->width();
          float h = viewScene->height();
 
              graphicsView->setScene(scene);
          delete viewScene;
 
              QPixmap pixmap = QPixmap::fromImage(image);
              scene->addPixmap(pixmap.scaled(QSize((int)w, (int)h, Qt::KeepAspectRatio, Qt::SmoothTransformation));
 
              qDebug() << "Width = " << w;
              qDebug() << "Height = " << h;
 
              graphicsView->show();
          }
      }

void MainWindow::loadGraphicsViewParameter(QGraphicsView *graphicsView)
      {
          QString fileName = QFileDialog::getOpenFileName(this,
                             tr("Open Image"), QDir::currentPath());
          if (!fileName.isEmpty())
          {
              QImage tempImage(fileName);
              if (tempImage.isNull())
              {
                  QMessageBox::information(this, tr("Load Warning"),
                                           tr("Cannot load %1.").arg(fileName));
                  return;
              }
              QImage image = tempImage.convertToFormat(QImage::Format_ARGB32);
              QGraphicsScene *scene = new QGraphicsScene;
              QGraphicsScene* viewScene = graphicsView->scene();
          float w = viewScene->width();
          float h = viewScene->height();

              graphicsView->setScene(scene);
          delete viewScene;

              QPixmap pixmap = QPixmap::fromImage(image);
              scene->addPixmap(pixmap.scaled(QSize((int)w, (int)h, Qt::KeepAspectRatio, Qt::SmoothTransformation));
       
              qDebug() << "Width = " << w;
              qDebug() << "Height = " << h;
         
              graphicsView->show();
          }
      }

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**sincnarf** · 18th September 2007, 12:07

didn't work. . . same windows error problem

**wysota** · 18th September 2007, 12:11

How about... using a debugger?

**sincnarf** · 18th September 2007, 15:47

what's a debugger? I'm using eclipse CDT plugin and I don't know how to debug this

**wysota** · 18th September 2007, 16:30

Debugger is a tool that let's you inspect the developped application while it's running. Among other things, it would tell you where exactly your application crashes. If you're using MinGW as a compiler using GDB for debugging is the best option.

**sincnarf** · 19th September 2007, 09:21

GDB says something like this... I can't understand...

Program received signal SIGSEGV, Segmentation fault.
0x00b2b2be in ZNK14QGraphicsScene9sceneRectEv ()
(gdb) backtrace
#0 0x00b2b2be in ZNK14QGraphicsScene9sceneRectEv ()
#1 0x00407453 in ?? ()
#2 0x0022b00c in ?? ()
#3 0x00000000 in ?? ()

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