Перерисовка изображения при нажатии на кнопку. Вызов paintEvent по кнопке

#ifndef PAINTING_H
#define PAINTING_H
#include <QPainter>
#include <QWidget>
 
class QPaintEvent;
 
class Painting: public QWidget
{
    Q_OBJECT
 
public:
 
 
    struct point {
      double  x,y;
    };
 
    std::vector <point> pointvector;
 
    Painting();
    ~Painting();
 
    void paintEvent(QPaintEvent *event);
};
 
#endif // PAINTING_H

#include "painting.h"
 
Painting::Painting()
{
      point p;
      p.x = 0;
      p.y = 0;
      pointvector.push_back(p);
      p.x = 500;
      p.y = 250;
      pointvector.push_back(p);
}
 
Painting::~Painting()
{
 
}
 
void Painting::paintEvent(QPaintEvent *)
{
    QPainter painter(this);
    painter.setPen(QPen(Qt::red,1,Qt::SolidLine));
    painter.drawLine(pointvector[0].x, pointvector[0].y, pointvector[1].x, pointvector[1].y);
}

#ifndef FORM_H
#define FORM_H
 
#include "painting.h"
#include <QPushButton>
#include <QLineEdit>
#include <QLabel>
#include <QGraphicsView>
#include <QWidget>
 
class Form : public QWidget
{
    Q_OBJECT
 
public:
    Form(QWidget *parent = 0);
    ~Form();
 
public slots:
 
private:
    QPushButton *  startButton;
 
    QLineEdit * x_1;
    QLineEdit * x_2;
    QLineEdit * y_1;
    QLineEdit * y_2;
 
    QLabel * x_1_label;
    QLabel * x_2_label;
    QLabel * y_1_label;
    QLabel * y_2_label;
 
    Painting * paintWidget;
};
 
#endif // FORM_H

#include "form.h"
#include "painting.h"
#include <QLayout>
 
Form::Form(QWidget *parent)
    : QWidget(parent)
{
    QPushButton *  startButton = new QPushButton("Start");
    QLineEdit * x_1 = new QLineEdit("10");
    QLineEdit * x_2 = new QLineEdit("500");
    QLineEdit * y_1 = new QLineEdit("50");
    QLineEdit * y_2 = new QLineEdit("50");
 
    QLabel * x_1_label = new QLabel("X1: ");
    QLabel * x_2_label = new QLabel("X2: ");
    QLabel * y_1_label = new QLabel("Y1: ");
    QLabel * y_2_label = new QLabel("Y2: ");
 
    Painting * paintWidget = new Painting();
 
    QVBoxLayout * VLayout  = new QVBoxLayout;
    QHBoxLayout * HLayout1 = new QHBoxLayout;
    QHBoxLayout * HLayout2 = new QHBoxLayout;
    QHBoxLayout * HLayout3 = new QHBoxLayout;
    QHBoxLayout * HLayout4 = new QHBoxLayout;
 
    HLayout1->addWidget(x_1_label);
    HLayout1->addWidget(x_1);
 
    HLayout2->addWidget(x_2_label);
    HLayout2->addWidget(x_2);
 
    HLayout3->addWidget(y_1_label);
    HLayout3->addWidget(y_1);
 
    HLayout4->addWidget(y_2_label);
    HLayout4->addWidget(y_2);
 
    VLayout->addLayout(HLayout1);
    VLayout->addLayout(HLayout2);
    VLayout->addLayout(HLayout3);
    VLayout->addLayout(HLayout4);
    VLayout->addWidget(startButton);
    VLayout->addWidget(paintWidget);
 
    QHBoxLayout * BasicLayout = new QHBoxLayout;
    BasicLayout->addLayout(VLayout);
 
    this->setLayout(BasicLayout);
 
    this->setMinimumHeight(500);
    this->setMinimumWidth(600);
    this->setMaximumHeight(500);
    this->setMaximumWidth(600);
 
    QObject::connect(startButton, SIGNAL(clicked()), this, SLOT(run()));
 
}
 
Form::~Form()
{
 
}

#include "form.h"
#include <QApplication>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Form w;
    w.show();
 
    return a.exec();
}