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();
}





#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






#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);
}

[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();
}
..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);


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 (http://doc.trolltech.com/4.4/examples.html#graphics-view) 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);
}

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....