QGraphicsView doesn't update on QComboBox SIGNAL

Hello, I'm having a little problem with a view that I have, I'm using the resizeEvent of the QMainWindow the view is in to call a function that redraws the view with a grid, so far so good, when I resize the window the view resizes along and the grid to. I also have a QComboBox that I use to choose the scale of the grid squares, the currentIndexChanged SIGNAL of the comboBox triggers a slot that calls the function that redraws the grid, but the view only updates after I resize the window again, it was suppose to update the view with the new grid scale as soon as the user changed the comboBox...?

This is a simplified version of the original that I did to make it easier to see the portion of the program which contains the fault, I tested it and the same behavior shows here...

main.h:

Code:

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#include <QApplication>
#include "maincontrol.h"
 
int main(int argc,char *argv[])
{
    QApplication a(argc,argv);
    MainControl m;
    m.show();
    m.setted=1;
    return a.exec();
}

---

maincontrol.h:

Code:

---

#ifndef MAINCONTROL_H
#define MAINCONTROL_H
 
#include <QMainWindow>
#include <QGraphicsView>
#include <QGraphicsScene>
#include <QComboBox>
#include <QPixmap>
#include <QImage>
#include <QResizeEvent>
#include <QLayout>
#include <QLabel>
 
class MainControl : public QMainWindow
{
    Q_OBJECT
public:
    explicit MainControl(QWidget *parent = 0);
 
    QHBoxLayout *combo_layout;
    QHBoxLayout *view_layout;
    QVBoxLayout *main_layout;
    QWidget *central_widget;
 
    QGraphicsView *control_view;
    QGraphicsScene *control_scene;
    QPixmap *control_pixmap;
    QComboBox *control_combobox;
    QLabel *debug_label;
    int SCALE;
    int image_w;
    int image_h;
    int setted;
    int set_pixel_value(int red,int green,int blue);
    void process_canvas();
protected:
    void resizeEvent(QResizeEvent *e);
signals:
 
public slots:
    void update_scale(int s);
 
};
 
#endif // MAINCONTROL_H

---

maincontrol.cpp:

Code:

---

#include "maincontrol.h"
 
MainControl::MainControl(QWidget *parent) :
    QMainWindow(parent)
{
    //----------------------initiate properties
    SCALE=10;
    image_w=300;
    image_h=300;
    setted=0;
    control_scene=new QGraphicsScene;
    control_view=new QGraphicsView(control_scene);
    control_view->setMinimumSize(image_w,image_h);
    control_view->setResizeAnchor(QGraphicsView::NoAnchor);
    control_view->setAlignment(Qt::AlignLeft|Qt::AlignTop);
 
    control_pixmap=new QPixmap;
    control_combobox=new QComboBox;
 
    QString c_str;
    int cc=1;
    while(cc<=10)
    {
    c_str.setNum(cc);
    control_combobox->addItem(c_str);
    cc++;
    }
    control_combobox->setCurrentIndex((SCALE/2)-1);
 
    combo_layout=new QHBoxLayout;
    view_layout=new QHBoxLayout;
    debug_label=new QLabel("");
    main_layout=new QVBoxLayout;
    central_widget=new QWidget;
 
    //----------------------set layouts
    combo_layout->addWidget(control_combobox);
    view_layout->addWidget(control_view);
 
    main_layout->addLayout(combo_layout);
    main_layout->addLayout(view_layout);
    main_layout->addWidget(debug_label);
    central_widget->setLayout(main_layout);
 
    this->setCentralWidget(central_widget);
 
    //----------------------draw image once
    process_canvas();
    control_scene->addPixmap(*control_pixmap);
    //----------------------connections
    connect(control_combobox,SIGNAL(currentIndexChanged(int)),this,SLOT(update_scale(int)));
}
//--------------------------------------- PROCESS CANVAS -----------------------------------------------//
//makes the image AND UPDATES it to the view
//Problem:When resizeEvent calls this function it updates the view as it should according to
//the it's last command (control_view->update()) but when update_scale calls it it doesn't update
//until I resize it again
void MainControl::process_canvas()
{
 QImage control_image(image_w,image_h,QImage::Format_RGB32);
 control_image.fill(set_pixel_value(0,0,0));
 int cy=0;
 int cx=0;
 while(cy<control_image.height())
 {
     while(cx<control_image.width())
     {
         if(cx%(10*SCALE)==0 || cy%(10*SCALE)==0)
         {
             control_image.setPixel(cx,cy,set_pixel_value(150,150,150));
         }
         cx++;
     }
     cx=0;
     cy++;
 }
 control_pixmap->convertFromImage(control_image.scaled(image_w,image_h));
 control_view->update();
}
//--------------------------------------- RESIZE EVENT -----------------------------------------------//
//The size of the image was suppose to go along with the view
void MainControl::resizeEvent(QResizeEvent *e)
{
if(setted)
{
    int new_w=e->size().width();
    int old_w=e->oldSize().width();
    int new_h=e->size().width();
    int old_h=e->oldSize().width();
 
    image_w+=new_w-old_w;
    image_h+=new_h-old_h;
    process_canvas();
}
}
//--------------------------------------- UPDATE SCALE -----------------------------------------------//
//It is called when the user changes the value of the comboBox
void MainControl::update_scale(int s)
{
SCALE=2*(s+1);
process_canvas();
}

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If you want to update the QGraphicsPixmapItem then you should keep a pointer to that and call setPixmap() with the new pixmap.

Cheers,
_

It worked, thank you so very much anda_skoa :D
Am I the one to mark as SOLVED thread?

Here is what I changed it after skoa's advice:

In maincontrol.h I declared a QGraphicsPixmapItem pointer to use with the QGraphicsScene:

Code:

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QGraphicsPixmapItem *control_pixmap_item;

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Then in the constructor I used:

Code:

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control_pixmap_item->setPixmap(*control)
control_scene->addItem(control_pixmap_item);

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Then on maincontrol.cpp I changed the update part in the process_canvas function:

Code:

---

void MainControl::process_canvas()
{
 QImage control_image(image_w,image_h,QImage::Format_RGB32);
 control_image.fill(set_pixel_value(0,0,0));
 int cy=0;
 int cx=0;
 while(cy<control_image.height())
 {
     while(cx<control_image.width())
     {
         if(cx%(10*SCALE)==0 || cy%(10*SCALE)==0)
         {
             control_image.setPixel(cx,cy,set_pixel_value(150,150,150));
         }
         cx++;
     }
     cx=0;
     cy++;
 }
 control_pixmap->convertFromImage(control_image.scaled(image_w,image_h));
control_pixmap_item->setPixmap(*control_pixmap);
 control_view->update();
}

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