QImage doesn't seem to load any images at all (always returning null)?

[SaldaVonSchwartz]

I'm on Windows7 and using Qt SDK 4.8.
Trying to read a file in with QImage but it just doesn't seem to load. That is, QImage(filename) or QImage(filename, "PNG") or QImage.load(filename) always return NULL.

Here's my code:

QString fileName = QFileDialog::getOpenFileName(this,
                                                    tr("Open Image"),
                                                    QDir::homePath(),
                                                    tr("Image Files (*.png *.tga *.bmp)"));
 
    if (!fileName.isEmpty())
    {
        targetImage = new QImage(fileName, "PNG");
        if(targetImage->isNull())
        {
            QMessageBox::information(this,
                                     tr("Viewer"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }
 
        onScreenImage.setBackgroundRole(QPalette::Base);
        onScreenImage.setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
        onScreenImage.setScaledContents(true);
        onScreenImage.setPixmap(QPixmap::fromImage(*targetImage));
    }
}

QString fileName = QFileDialog::getOpenFileName(this,
                                                    tr("Open Image"),
                                                    QDir::homePath(),
                                                    tr("Image Files (*.png *.tga *.bmp)"));

    if (!fileName.isEmpty())
    {
        targetImage = new QImage(fileName, "PNG");
        if(targetImage->isNull())
        {
            QMessageBox::information(this,
                                     tr("Viewer"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }

        onScreenImage.setBackgroundRole(QPalette::Base);
        onScreenImage.setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
        onScreenImage.setScaledContents(true);
        onScreenImage.setPixmap(QPixmap::fromImage(*targetImage));
    }
}

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What am I doing wrong?

[Berryblue031]

targetImage = new QImage(fileName, "PNG");

targetImage = new QImage(fileName, "PNG");

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Remove the optional format parameter ("PNG") and just use the default so QImage will autodetect the file type otherwise you need to filter QFileDialog only to png files

QString fileName = QFileDialog::getOpenFileName(...

QString fileName = QFileDialog::getOpenFileName(...

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What is the value of fileName here? For QImage you will need the full path not just the fileName.

[Ricardo_arg]

onScreenImage.setPixmap(QPixmap::fromImage(*target Image));
i think you have to cahnge this. hope it helps
onScreenImage.setPixmap(QPixmap::fromImage(targetI mage));

[ChrisW67]

Comments embedded:

QString fileName = QFileDialog::getOpenFileName(this,
                                                    tr("Open Image"),
                                                    QDir::homePath(),
                                                    tr("Image Files (*.png *.tga *.bmp)"));
// you could have a BMP or Targa file at this point
// Qt has no Targa format support out of the box
    if (!fileName.isEmpty())
    {
        targetImage = new QImage(fileName, "PNG"); 
// Not much good if the file is not a PNG
// You allocate memory you do not free: memory leak
// No need for this to be on the heap at all
 
        if(targetImage->isNull())
        {
            QMessageBox::information(this,
                                     tr("Viewer"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }
 
        onScreenImage.setBackgroundRole(QPalette::Base);
        onScreenImage.setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
        onScreenImage.setScaledContents(true);
        onScreenImage.setPixmap(QPixmap::fromImage(*targetImage));
// Why did you use a QImage if you require a QPixmap ultimately?
    }
}

QString fileName = QFileDialog::getOpenFileName(this,
                                                    tr("Open Image"),
                                                    QDir::homePath(),
                                                    tr("Image Files (*.png *.tga *.bmp)"));
// you could have a BMP or Targa file at this point
// Qt has no Targa format support out of the box
    if (!fileName.isEmpty())
    {
        targetImage = new QImage(fileName, "PNG"); 
// Not much good if the file is not a PNG
// You allocate memory you do not free: memory leak
// No need for this to be on the heap at all

        if(targetImage->isNull())
        {
            QMessageBox::information(this,
                                     tr("Viewer"),
                                     tr("Cannot load %1.").arg(fileName));
            return;
        }

        onScreenImage.setBackgroundRole(QPalette::Base);
        onScreenImage.setSizePolicy(QSizePolicy::Ignored, QSizePolicy::Ignored);
        onScreenImage.setScaledContents(true);
        onScreenImage.setPixmap(QPixmap::fromImage(*targetImage));
// Why did you use a QImage if you require a QPixmap ultimately?
    }
}

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You don't say if it is failing in the development or deployed environment. None of this will work deployed unless you also deploy the necessary imageformat plugins. What does QImageReader::supportedImageFormats() return?