Multiple use of QGraphicScene

[Xtresis]

Hi all,

I'm quite new here and just started with Qt for a couple of days. Currently I'm working on my first project with Qt and I'm trying to draw some kind of map where a few red dots will become visible after putting data in a table.

I've already created a ui in Qt with a QGraphicsView included. Then created a QGraphicsScene named 'scene'. In that scene i draw a few circles and lines with the following code:

//draw map
void Unknown::drawMap(int width)
{
    QGraphicsScene *scene = new QGraphicsScene;
    scene->setSceneRect(0, 0, width, width);
    scene->setBackgroundBrush(Qt::white);
 
    //draw horizontal & vertical line
    scene->addLine(0, (width/2), width, (width/2));
    scene->addLine((width/2), 0, (width/2), width);
 
    //draw 5 circles
    int x = (width/12), y = width-(width/6);
    for(int i=0; i<5; i++)
    {
        scene->addEllipse(x, x, y, y, QColor(180, 180, 180), Qt::NoBrush);
        x = x + (width/12);
        y = y - (width/6);
    }
 
    //put scene on screen
 
    ui->graphicsView->setScene(scene);

//draw map
void Unknown::drawMap(int width)
{
    QGraphicsScene *scene = new QGraphicsScene;
    scene->setSceneRect(0, 0, width, width);
    scene->setBackgroundBrush(Qt::white);

    //draw horizontal & vertical line
    scene->addLine(0, (width/2), width, (width/2));
    scene->addLine((width/2), 0, (width/2), width);

    //draw 5 circles
    int x = (width/12), y = width-(width/6);
    for(int i=0; i<5; i++)
    {
        scene->addEllipse(x, x, y, y, QColor(180, 180, 180), Qt::NoBrush);
        x = x + (width/12);
        y = y - (width/6);
    }

    //put scene on screen

    ui->graphicsView->setScene(scene);

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This works like a charm. However, when this function is finished I would like to add some red dots to this QGraphicsScene with a different function.

//draw dot
void Unknown::drawDot()
{
    scene->addEllipse(50, 50, 1, 1, QColor(255, 0, 0), Qt::NoBrush);
    ui->graphicsView->setScene(scene);
}

//draw dot
void Unknown::drawDot()
{
    scene->addEllipse(50, 50, 1, 1, QColor(255, 0, 0), Qt::NoBrush);
    ui->graphicsView->setScene(scene);
}

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When applying this function to the main program and build it, I get the error: "scene not declared". I do understand why, but I don't know how to solve this problem without getting errors. I already tried the following in the main program:

#include "unknown.h"
#include "ui_unknown.h"
 
QGraphicsScene *scene = new QGraphicsScene;

#include "unknown.h"
#include "ui_unknown.h"

QGraphicsScene *scene = new QGraphicsScene;

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When adding this to the program, the building process completes succesfully. The program shuts down immediately though.

Can someone help me out here?

[wysota]

The scene variable in yourd drawMap() is local to the method. Make it a member of your class and everything will be fine. This is a lack-of-C++-skills problem, you know...

[Xtresis]

Thanks for you reply. I know indeed that this is a lack-of-C++-skills, but I can't figure out how to fix this problem ( and that's why I put this in the Newbie subforum ). I would really appriciate an example how to solve this is the right way.

Thank you!

[nish]

if you dont want to make it a member than you can access the scene by calling

//draw dot
void Unknown::drawDot()
{
    //scene->addEllipse(50, 50, 1, 1, QColor(255, 0, 0), Qt::NoBrush);
    ui->graphicsView->scene()->addEllipse(50, 50, 1, 1, QColor(255, 0, 0), Qt::NoBrush);
    //We already set this in previous function so no need now
   //ui->graphicsView->setScene(scene);
}

//draw dot
void Unknown::drawDot()
{
    //scene->addEllipse(50, 50, 1, 1, QColor(255, 0, 0), Qt::NoBrush);
    ui->graphicsView->scene()->addEllipse(50, 50, 1, 1, QColor(255, 0, 0), Qt::NoBrush);
    //We already set this in previous function so no need now
   //ui->graphicsView->setScene(scene);
}

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but as suggested you should learn to make a class.

[Xtresis]

Thank you for your reply. Your solution works indeed, but I will try it with a class as well. Already found someone in my study book, so I think that shouldn't be a problem.