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Weird problem, with MainWindow class variables.

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  • R Offline
    R Offline
    Rondog
    wrote on last edited by
    #7

    I ran into something similar to this recently when trying to update a value by reference. In my case it was done this way for a very different reason but otherwise it was similar to what you are doing.

    I would suggest you re-write your access functions like this:

    @
    int MainWindow::GetImageHeight(void) {return imageHeight;}
    int MainWindow::GetImageWidth(void) {return imageWidth; }
    @

    You can use them like this:

    @
    MainWindow mw;
    int width, height;

    height = mw.GetImageHeight();
    width = mw.GetImageWidth();
    

    @

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    • A Offline
      A Offline
      AndreasA9
      wrote on last edited by
      #8

      I have already tried this.

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      • R Offline
        R Offline
        Rondog
        wrote on last edited by
        #9

        In your code you have this:

        @
        QApplication a(argc, argv);
        MainWindow w;
        Own own;
        ...
        @

        These exist only in main() which will run until a.exec() returns. For the classes 'w' and 'own' is there a pointer, or some other reference to these classes that you can use outside of main()?

        For this code:

        @
        MainWindow mw;
        int width, height;

            height = mw.GetImageHeight();
            width = mw.GetImageWidth();
        

        @

        GetImageHeight() and GetImageWidth() should return zero or possibly some other random value as it is another, unrelated class.

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        • A Offline
          A Offline
          AndreasA9
          wrote on last edited by
          #10

          Sorry, i don't understand, what you are trying to say to me.

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          • A Offline
            A Offline
            andreyc
            wrote on last edited by
            #11

            In your example (below), are you trying to get width and height from MainWindow before app.exec() ?
            @
            MainWindow mw;
            int width, height;

                mw.GetImageHeight(height);
                mw.GetImageWidth(width);
            

            @

            If so then MainWindow::imageHeight and imageWidth are not initialized and you are getting whatever random numbers are there.

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            • A Offline
              A Offline
              AndreasA9
              wrote on last edited by
              #12

              No, im not trying to get them before app.exec()
              getImageHeight and getImageWidth are exectued after i press a button on my form and long proccess is done with network communication is done

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              • A Offline
                A Offline
                AndreasA9
                wrote on last edited by
                #13

                I post my full source code here

                mainwindow.h
                @
                #ifndef MAINWINDOW_H
                #define MAINWINDOW_H

                #include <QMainWindow>
                #include "networking.h"
                namespace Ui {
                class MainWindow;
                }

                class MainWindow : public QMainWindow
                {
                Q_OBJECT

                public:

                explicit MainWindow(QWidget *parent = 0);
                void GetImageHeight(int &height);
                void GetImageWidth(int &width);
                
                ~MainWindow();
                

                private slots:

                void on_pushButton_clicked();
                void on_WidthSlider_valueChanged(int value);
                void on_HeightSlider_valueChanged(int value);
                

                private:
                int imageWidth;
                int imageHeight;

                QUrl q;
                Ui::MainWindow *ui;
                

                };

                #endif // MAINWINDOW_H

                @

                networking.h

                @
                #ifndef NETWORKING_H
                #define NETWORKING_H

                #include <QtNetwork/QNetworkAccessManager>
                #include <QtNetwork/QNetworkRequest>
                #include <QMessageBox>
                #include "mainwindow.h"

                class networking : public QObject
                {
                Q_OBJECT

                public:
                    networking();
                
                    void on_download_triggered(QUrl url);
                    bool IsNetworkAvailable();
                
                
                private:
                    QNetworkAccessManager *manager = new QNetworkAccessManager(this);
                    void ProcessPicture(QImage *image);
                

                private slots:
                void onNetworkReply(QNetworkReply* reply);

                };

                #endif // NETWORKING_H

                @

                mainwindow.cpp

                @#include "mainwindow.h"
                #include "ui_mainwindow.h"

                MainWindow::MainWindow(QWidget *parent) :
                QMainWindow(parent),
                ui(new Ui::MainWindow)
                {

                ui->setupUi(this);
                this->setFixedSize(378, 304);
                

                }

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

                void MainWindow::on_pushButton_clicked()
                {

                if(ui->URLbox->text().isEmpty()) QMessageBox::information(0, "Warning", "No URL inserted!");
                
                else
                {
                    networking *n = new networking();
                    q = ui->URLbox->text();
                    if(n->IsNetworkAvailable()) n->on_download_triggered(q);
                }
                

                }

                void MainWindow::GetImageHeight(int &height) {height = imageHeight;}

                void MainWindow::GetImageWidth(int &width) {width = imageWidth; }

                void MainWindow::on_WidthSlider_valueChanged(int value)
                {
                imageWidth = value;
                QString valueString = QString::number(value);
                ui->WidthLabel->setText(valueString);
                }

                void MainWindow::on_HeightSlider_valueChanged(int value)
                {
                imageHeight = value;
                QString valueString = QString::number(value);
                ui->HeightLabel->setText(valueString);
                }

                @

                networking.cpp

                @#include "networking.h"
                #include <QtNetwork/QNetworkReply>
                #include <QFileDialog>

                networking::networking()
                {
                connect(manager, SIGNAL(finished(QNetworkReply*)), this, SLOT(onNetworkReply(QNetworkReply*)));
                }
                void networking::on_download_triggered(QUrl url)
                {
                manager->get(QNetworkRequest(QUrl(url)));
                }

                void networking::ProcessPicture(QImage *image)
                {
                MainWindow *mw = new MainWindow();

                int width, height;
                
                mw->GetImageHeight(height);
                mw->GetImageWidth(width);
                
                
                qDebug() << height;
                qDebug() << width;
                
                QImage newimage = image->scaled(width, height, Qt::KeepAspectRatio);
                QString path =  QFileDialog::getSaveFileName(0, tr("Save Image"), "C://", tr("Image Files (*.png *.jpg *.bmp)"));
                
                newimage.save(path);
                

                }

                void networking::onNetworkReply(QNetworkReply* reply)
                {
                if(!reply->error())
                {
                QImage *img = new QImage();
                img->loadFromData(reply->readAll());

                    if(img->isNull())
                            QMessageBox::critical(0, "Error", "Inserted URL is not an image!");
                
                    ProcessPicture(img);
                
                }
                else
                {
                    QVariant statusCode = reply->attribute(QNetworkRequest::HttpStatusCodeAttribute);
                    int status = statusCode.toInt();
                
                    qDebug() << status;
                
                    switch(status)
                    {
                        case 0:
                        {
                            QMessageBox::critical(0, "Error", "URL doesn't exist!");
                            break;
                        }
                        case 404:
                        {
                            QMessageBox::critical(0, "Error", "404 not found!");
                            break;
                        }
                    }
                }
                

                }

                bool networking::IsNetworkAvailable()
                {
                QNetworkAccessManager m;
                QNetworkReply *check = m.get(QNetworkRequest(QUrl("google.com")));
                return (!check->error()) ? true : false;
                }
                @

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                • R Offline
                  R Offline
                  Rondog
                  wrote on last edited by
                  #14

                  I think this is your problem:

                  @
                  void networking::ProcessPicture(QImage *image)
                  {
                  MainWindow *mw = new MainWindow();

                  int width, height;
                  
                  mw->GetImageHeight(height);
                  mw->GetImageWidth(width);
                  
                  qDebug() << height;
                  qDebug() << width;
                  

                  ...
                  }
                  @

                  The class '*mw' is unrelated to the mw class created in main(). The member imageWidth and imageHeight are not updated in this version.

                  To verify this you could create a global pointer of the MainWindow class and see if this solves the problem:

                  @
                  MainWindow *g_mw;

                  int main(int argc, char *argv[])
                  {
                      QApplication a(argc, argv);
                      MainWindow w;
                      Own own;
                  
                      g_mw = &mw;
                  
                   
                      QObject::connect(&w, SIGNAL(heightValueChanged(int)), &own, SLOT(imageHeight(int)));
                      QObject::connect(&w, SIGNAL(widthValueChanged(int)), &own, SLOT(imageWidth(int)));
                   
                      w.show();
                   
                      return a.exec&#40;&#41;;
                  }
                  

                  @

                  and then in your network module

                  @
                  #include "networking.h"
                  #include <QtNetwork/QNetworkReply>
                  #include <QFileDialog>

                  extern MainWindow *g_mw;

                  networking::networking()
                  {
                  ...
                  }
                  ...
                  void networking::ProcessPicture(QImage *image)
                  {
                  // MainWindow *mw = new MainWindow();

                  int width, height;
                  
                  g_mw->GetImageHeight(height);
                  g_mw->GetImageWidth(width);
                  
                  
                  qDebug() << height;
                  qDebug() << width;
                  

                  ...
                  }
                  @

                  Note: I wouldn't use a global variable like this. You are better to pass a pointer (maybe as part of the constructor of your Networking class?). It is just a simple way to verify this is the problem without changing too much.

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                  • A Offline
                    A Offline
                    andreyc
                    wrote on last edited by
                    #15

                    Rondog is right. You are creating new MainWindow object and it is not related to your main MainWindow.

                    Another option to solve it would be to pass a MainWindow pointer to networking ctor and keep it there. Then in networking::ProcessPicture() use that pointer.
                    networking.h

                    @
                    #ifndef NETWORKING_H
                    #define NETWORKING_H

                    class MainWindow;
                     
                    class networking : public QObject
                    {
                    

                    ...
                    public:
                    networking(MainWindow* mw);

                    ...
                    private:
                    MainWindow* m_mw;

                    };
                    #endif // NETWORKING_H
                    

                    @

                    networking.cpp
                    @
                    #include "networking.h"
                    #include "MainWindow.h"
                    #include <QtNetwork/QNetworkReply>
                    #include <QFileDialog>

                    networking::networking(MainWindow* mw) : m_mw(mw)
                    {
                    

                    ...
                    }

                    void networking::ProcessPicture(QImage *image)
                    {
                    // MainWindow *mw = new MainWindow();

                    int width, height;
                    
                    m_mw->GetImageHeight(height);
                    m_mw->GetImageWidth(width);
                    
                    
                    qDebug() << height;
                    qDebug() << width;
                    

                    ...
                    }
                    @

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                    • A Offline
                      A Offline
                      AndreasA9
                      wrote on last edited by
                      #16

                      Thanks, it worked! I didn't know, why i didn't realise fault myself. Quite logical. Thanks again!

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                      • A Offline
                        A Offline
                        AndreasA9
                        wrote on last edited by
                        #17

                        One last question, why i had to write class MainWindow; to my networking.h file.

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                        • A Offline
                          A Offline
                          andreyc
                          wrote on last edited by
                          #18

                          It is a forward declaration. Compiler needs to know that a type exists but does not need to know the details. It works with the pointers and the references. Helps to avoid including unneeded headers.

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