The program freezes when an instance of a class is created

gabor53

Hi,
I have the following code to display an image:

void MainWindow::on_tableView_clicked(const QModelIndex &index)
{
    int row = index.row ();
    int column = index.column ();
    qDebug() << "Index: " << "(" << row <<"," << column << ")";

    if(column == 2)
        {
            qDebug() << "Column 2 was chosen.";

            QPixmap imageToEnlarge = index.data(Qt::DecorationRole).value<QPixmap>();

	    ImageDisplay *mImageDisplay = new ImageDisplay(this);
            mImageDisplay->viewImage(imageToEnlarge);
        }
}

The called function:

void ImageDisplay::viewImage(QPixmap imageToEnlarge)
{
    int w = ui->ImageLabel->width ();
    int h = ui->ImageLabel->height ();
    ui->ImageLabel->setPixmap (imageToEnlarge.scaled(w,h,Qt::KeepAspectRatio));
}

When program execution reaches ImageDisplay * freezes and crashes the program. What did I do incorrectly? Thank you for your help.

hskoglund

Hi, maybe the QPixmap wasn't set correctly in your model's data() function? You could check if imageToEnlarge is null, then don't proceed.

L_Raiz

I'd try to pass imageToEnlarge argument by reference instead of value. Maybe something bad is going on when copying it during the call.

Paul Colby

What does the ImageDisplay constructor look like?

gabor53

@Paul-Colby

#ifndef IMAGEDISPLAY_H
#define IMAGEDISPLAY_H

#include <mainwindow.h>
#include <additem.h>
#include <review.h>
#include <QDialog>

namespace Ui {
class ImageDisplay;
}

class ImageDisplay : public QDialog
{
    Q_OBJECT

public:
    explicit ImageDisplay(QWidget *parent = 0);
    ~ImageDisplay();
    void viewImage(QPixmap imageToEnlarge );

private:
    Ui::ImageDisplay *ui;
};

#endif // IMAGEDISPLAY_H

gabor53

Now it also sends a SIGSEGV error.

gabor53

It also displays the following messages:
can't find linker symbol for virtual table for QPixmap' value found _q_ObjectMutexPool' instead
can't find linker symbol for virtual table for QPixmap' value found _q_ObjectMutexPool' instead
Column 2 was chosen.
can't find linker symbol for virtual table for QPixmap' value found _q_ObjectMutexPool' instead
can't find linker symbol for virtual table for QPixmap' value found _q_ObjectMutexPool' instead

jsulm

@gabor53 Can you please show the content of the ImageDisplay constructor, not just its declaration?

gabor53

@jsulm
Here it is:

#include "imagedisplay.h"
#include "ui_imagedisplay.h"

ImageDisplay::ImageDisplay(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::ImageDisplay)
{
    ui->setupUi(this);

    ImageDisplay(imageToEnlarge);
}

ImageDisplay::~ImageDisplay()
{
    delete ui;
}

void ImageDisplay::viewImage(QPixmap imageToEnlarge)
{
    int w = ui->ImageLabel->width ();
    int h = ui->ImageLabel->height ();
    ui->ImageLabel->setPixmap (imageToEnlarge.scaled(w,h,Qt::KeepAspectRatio));
}

Thank you.

mrjj

ImageDisplay::ImageDisplay(QWidget *parent) :
QDialog(parent),
ui(new Ui::ImageDisplay)
{
ui->setupUi(this);
ImageDisplay(imageToEnlarge); <<<<<< Call ctor again !! ?!

should that not be viewImage(QPixmap imageToEnlarge) ?

jsulm

@gabor53 To add to @mrjj: what is imageToEnlarge in

ImageDisplay::ImageDisplay(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::ImageDisplay)
{
    ui->setupUi(this);

    ImageDisplay(imageToEnlarge);
}

kshegunov

How does this even compile? You're not allowed to call constructors explicitly ... probably it creates a temporary ...

VRonin

@kshegunov said in The program freezes when an instance of a class is created:

How does this even compile?

another problem is that in the constructor imageToEnlarge should be an undefined symbol. if it is defined in that constructor then there is a naming conflict in viewImage. this should 100% not compile

gabor53

ImageDisplay::ImageDisplay(QWidget *parent) :
    QDialog(parent),
    ui(new Ui::ImageDisplay)
{
    ui->setupUi(this);

    ImageDisplay(imageToEnlarge);
}

ImageDisplay::~ImageDisplay()

I deleted ImageDisplay(imageToEnlarge). As a result it doesn't freeze but doesn't display the image I clicked on either.

josephdp

As what others suggested, the content of the form constructor is wrong.
Your widgets are already taken care of by setupUI().
Thus, the logic of displaying the image should just be in viewImage ().

QPixmap imageToEnlarge = index.data(Qt::DecorationRole).value<QPixmap>();

where is the data in this?

here's a brief example using QT's QImage.

QPixmap scaledPixmap = QPixmap::fromImage (image).scaled (
    QSize (w, h),
    Qt::IgnoreAspectRatio, Qt::SmoothTransformation);

ui->ImageLabel->setPixmap (scaledPixmap);

gabor53

The following seems to work:

void MainWindow::on_tableView_clicked(const QModelIndex &index)
{
    int row = index.row ();
    int column = index.column ();
    qDebug() << "Index: " << "(" << row <<"," << column << ")";

    if(column == 2)
        {
            qDebug() << "Column 2 was chosen.";

            QPixmap imageToEnlarge = index.data(Qt::DecorationRole).value<QPixmap>();

            int w = ui->label_Temp->width();
            int h = ui->label_Temp->height ();
            ui->label_Temp->setPixmap (imageToEnlarge.scaled(w,h,Qt::KeepAspectRatio));
            ImageDisplay *mImageDisplay = new ImageDisplay;
            mImageDisplay->viewImage(imageToEnlarge);
            mImageDisplay->exec ();

        }
}

Thank you for your help.

mrjj

super
You should get rid of new or add a delete

ImageDisplay *mImageDisplay = new ImageDisplay;
mImageDisplay->viewImage(imageToEnlarge);
mImageDisplay->exec ();
delete ImageDisplay; /// clean up

or simply dont use new as you use exec()

ImageDisplay mImageDisplay;
mImageDisplay.viewImage(imageToEnlarge);
mImageDisplay.exec ();

gabor53

Thank you!!