QPaint Class and QGraphicsScene ....I am stuck !!

[salmanmanekia]

Hi,

I have written a program to show some buttons and use QGraphicsscene and paint class but when i run this program the output is only a 'WHITE BLANK SCREEN '

Below is the implementation of this class and main function,any help/suggestion would be welcome.....pls give it a look !!

int main(int argc,char *argv[]) 
{
    QApplication app(argc, argv);
 
    paintClass paint;
    paint.addScene();
    paint.setIcons();
    paint.drawBGround();
    paint.show();
 
 
    return app.exec();
}

int main(int argc,char *argv[]) 
{
    QApplication app(argc, argv);

    paintClass paint;
    paint.addScene();
    paint.setIcons();
    paint.drawBGround();
    paint.show();


    return app.exec();
}

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#ifndef PAINTCLASS_H
#define PAINTCLASS_H
 
#include <QGraphicsScene>
#include <QGraphicsView>
 
#include <QGraphicsItem>
#include <QGraphicsEllipseItem>
 
#include <QCursor>
#include <QRectF>
 
#include <QPushButton>
#include <QGraphicsProxyWidget>
 
#include <QIcon>
 
#include <QVBoxLayout>
 
#include <QPainter>
#include <QWidget>
 
class paintClass:public QPainter,public QGraphicsView 
{
    public:
        QRectF r1;
        QRectF r2;
        QGraphicsItem *parent;
        QPainter painter;
        QGraphicsScene scene;
        QWidget *widg ;
        QPushButton *stopButton;
        QPushButton *playButton;
        QHBoxLayout *hLayout;
        QGraphicsProxyWidget *proxy;
 
        paintClass(QGraphicsView *parent = 0);
        void drawBGround();
        void addScene();
        void setIcons();
};
 
#endif

#ifndef PAINTCLASS_H
#define PAINTCLASS_H

#include <QGraphicsScene>
#include <QGraphicsView>

#include <QGraphicsItem>
#include <QGraphicsEllipseItem>

#include <QCursor>
#include <QRectF>

#include <QPushButton>
#include <QGraphicsProxyWidget>

#include <QIcon>

#include <QVBoxLayout>

#include <QPainter>
#include <QWidget>

class paintClass:public QPainter,public QGraphicsView 
{
    public:
        QRectF r1;
        QRectF r2;
        QGraphicsItem *parent;
        QPainter painter;
        QGraphicsScene scene;
        QWidget *widg ;
        QPushButton *stopButton;
        QPushButton *playButton;
        QHBoxLayout *hLayout;
        QGraphicsProxyWidget *proxy;

        paintClass(QGraphicsView *parent = 0);
        void drawBGround();
        void addScene();
        void setIcons();
};

#endif

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#include "paintClass.h"
 
paintClass::paintClass(QGraphicsView *parent):QGraphicsView(parent) 
{
    r1.setRect(100,200,100,160);
    r2.setRect(0,0,300,300);
    widg = new QWidget;
    stopButton = new QPushButton;
    playButton = new QPushButton;
    hLayout = new QHBoxLayout;
}
 
void paintClass::drawBGround() 
{
    painter.setPen(Qt::black);
    scene.addText("Hello, world!");
    scene.setBackgroundBrush(Qt::blue);
}
 
void paintClass::addScene() 
{
    scene.addText("Hello, world!");
 
    hLayout->addWidget(stopButton);
    hLayout->addWidget(playButton);
    widg->setLayout(hLayout);
    scene.addWidget(widg);
}
 
void paintClass::setIcons() 
{
    playButton->setIcon(QIcon("./pics/play.JPG"));
    stopButton->setIcon(QIcon("./pics/stop.JPG"));
 
    QGraphicsView view(&scene);
}

#include "paintClass.h"

paintClass::paintClass(QGraphicsView *parent):QGraphicsView(parent) 
{
    r1.setRect(100,200,100,160);
    r2.setRect(0,0,300,300);
    widg = new QWidget;
    stopButton = new QPushButton;
    playButton = new QPushButton;
    hLayout = new QHBoxLayout;
}

void paintClass::drawBGround() 
{
    painter.setPen(Qt::black);
    scene.addText("Hello, world!");
    scene.setBackgroundBrush(Qt::blue);
}

void paintClass::addScene() 
{
    scene.addText("Hello, world!");

    hLayout->addWidget(stopButton);
    hLayout->addWidget(playButton);
    widg->setLayout(hLayout);
    scene.addWidget(widg);
}

void paintClass::setIcons() 
{
    playButton->setIcon(QIcon("./pics/play.JPG"));
    stopButton->setIcon(QIcon("./pics/stop.JPG"));

    QGraphicsView view(&scene);
}

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[jpn]

The code above is not very well structured. It almost looks like you are randomly trying things. You should start with going through the Qt tutorial. Then, you can take a look at graphics view examples.

[Brandybuck]

There is a new Graphics View webcast from ICS Network. It is available for viewing online, or video download. You can find it at: <http://www.ics.com/icsnetwork/>. There is also a brand new thread for the webcast here at QtCenter: <http://www.qtcentre.org/forum/f-icsnetwork-25.html>.

This is a good place to start learning about Qt's Graphics View framework, starting with a simple "hello world" program and advancing to animation and optimization.

[salmanmanekia]

Hi..
thanks for the reply ..i have just starting streaming the video..i hope it would be helpful...any ways ,the problem with this code is more with the class structure i think (as mentioned by jpn ),initialy i was trying these things in the main function and all was working nice but then i had to use QT'S drawBackground() function which is virtual and protected so i had to create a class in which i could be using it...so...the code in main which looks like this works fine...

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>
 
#include <QGraphicsItem>
#include <QGraphicsEllipseItem>
 
#include <QCursor>
#include <QRectF>
 
#include <QPushButton>
#include <QGraphicsProxyWidget>
 
#include <QIcon>
 
#include <QVBoxLayout>
 
#include <QPainter>
 
#include "paintClass.h"
 
int main(int argc,char *argv[])
{
  QApplication app(argc, argv);
 
  QGraphicsScene scene;
 
  const QRectF r1(100,200,100,160);
  const QRectF r2(0,0,300,300);
 
 
  QGraphicsItem *parent = 0;
  QGraphicsEllipseItem ellipseItem(r1,parent);
  ellipseItem.setFlag(QGraphicsItem::ItemIsFocusable,true);
  ellipseItem.setSelected(true);
 
  ellipseItem.setVisible(true);
 
  scene.addItem(&ellipseItem);
 
   scene.addText("Hello, world!");
 
  QWidget *widg = new QWidget;
  QPushButton *stopButton = new QPushButton;
  stopButton->setIcon(QIcon("C:/pics/stop.JPG"));
 
  QPushButton *playButton = new QPushButton;
  playButton->setIcon(QIcon("C:/pics/play.JPG"));
 
  QHBoxLayout *hLayout = new QHBoxLayout;
  hLayout->addWidget(stopButton);
  hLayout->addWidget(playButton);
  widg->setLayout(hLayout);
  QGraphicsProxyWidget *proxy = scene.addWidget(widg);
 
  paintClass *paint ;
  paint->drawBGround(&scene);
 
  QGraphicsView view(&scene);
  view.show();
 
  return app.exec();
}

#include <QApplication>
#include <QGraphicsScene>
#include <QGraphicsView>

#include <QGraphicsItem>
#include <QGraphicsEllipseItem>

#include <QCursor>
#include <QRectF>

#include <QPushButton>
#include <QGraphicsProxyWidget>

#include <QIcon>

#include <QVBoxLayout>

#include <QPainter>

#include "paintClass.h"

int main(int argc,char *argv[])
{
  QApplication app(argc, argv);
  
  QGraphicsScene scene;
    
  const QRectF r1(100,200,100,160);
  const QRectF r2(0,0,300,300);
  
  
  QGraphicsItem *parent = 0;
  QGraphicsEllipseItem ellipseItem(r1,parent);
  ellipseItem.setFlag(QGraphicsItem::ItemIsFocusable,true);
  ellipseItem.setSelected(true);
  
  ellipseItem.setVisible(true);
  
  scene.addItem(&ellipseItem);
  
   scene.addText("Hello, world!");
 
  QWidget *widg = new QWidget;
  QPushButton *stopButton = new QPushButton;
  stopButton->setIcon(QIcon("C:/pics/stop.JPG"));
  
  QPushButton *playButton = new QPushButton;
  playButton->setIcon(QIcon("C:/pics/play.JPG"));
  
  QHBoxLayout *hLayout = new QHBoxLayout;
  hLayout->addWidget(stopButton);
  hLayout->addWidget(playButton);
  widg->setLayout(hLayout);
  QGraphicsProxyWidget *proxy = scene.addWidget(widg);
    
  paintClass *paint ;
  paint->drawBGround(&scene);
  
  QGraphicsView view(&scene);
  view.show();
  
  return app.exec();
}

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..and in my first post the code is almost same except that (i think so )the class is not properly called...any advice would be welcomed...thanks again ...!!1

[jpn]

the code in main which looks like this works fine...

paintClass *paint ;
paint->drawBGround(&scene);

paintClass *paint ;
paint->drawBGround(&scene);

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Are you sure?

[salmanmanekia]

sorry man ...i forgot to comment it...!!...you know , for now there is no paintClass ..so ...
// 1. paintClass *paint ;
// 2. paint->drawBGround(&scene);
and everything works fine....

[jpn]

So, have you looked at graphics view examples and did you see the webcast as proposed? It makes no sense inherit something from QPainter and QGraphicsView. Also, writing something like:

{
    ...
    QGraphicsView view(&scene);
}

{
    ...
    QGraphicsView view(&scene);
}

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has no effect at all. The QGraphicsView object gets immediately destructed, according to normal C++ rules.

I would recommend taking one of the graphics view examples as a base. That would give you a properly constructed base where you can start adding your own things.

[salmanmanekia]

yes i have taken look at webcast ....what i think is that ,that i can understand the graphic related api in qt,the problem lies in how to manage classes ,in this case its graphics ...it could have been a network related api and i would have the same problem...
still i understand that this statement executes and ends at the same time...so no effect at all
1. {
2. ...
3. QGraphicsView view(&scene);
4. }

can you guide me to some good resource/tutorial for the class heirachy like how inheritance works in qt ...also if you can pinpoint the wrong things/concept which i have in my code ,so that i can look into solution to that..!!!!..because i am still not crystal clear that wht the problem is what exactly is the way to solve it...thanks again....