#ifndef DRAWWIDGET_H
#define DRAWWIDGET_H

#include <QtGui>

class DrawWidget : public QGraphicsView{

public:
    DrawWidget(QWidget *parent = 0);

protected:
    void paintEvent(QPaintEvent *event);

private:

};

#endif // DRAWWIDGET_H

drawwidget.cpp

#include "DrawWidget.h"
#include <QtGui>

DrawWidget::DrawWidget(QWidget* parent):
        QGraphicsView(parent)
{

}


void DrawWidget::paintEvent(QPaintEvent *event)
{
    QPainter painter(this);
    painter.drawLine(10, 10, 40, 50);

}

#include <QtGui/QApplication>
#include "dialog.h"
#include "DrawWidget.h"

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

    QWidget pWidget;
    DrawWidget pView(&pWidget);
    QVBoxLayout pLayout;
    pLayout.addWidget(&pView);

    pView.show();
    pWidget.setLayout(&pLayout);
    pWidget.show();

    return a.exec();
}