I can not get a red window

[rezas1000]

Hello
I can not get a red window pleaze help me.

#ifndef E_H
#define E_H
 
#include <QtWidgets>
 
class paint : public QWidget
{
  Q_OBJECT
 
  public:
    paint(QWidget *parent = 0);
 
  protected:
    void paintEvent(QPaintEvent *event);
    void drawLines(QPainter *qp);
 
};
#endif // E_H

#ifndef E_H
#define E_H

#include <QtWidgets>

class paint : public QWidget
{
  Q_OBJECT

  public:
    paint(QWidget *parent = 0);

  protected:
    void paintEvent(QPaintEvent *event);
    void drawLines(QPainter *qp);

};
#endif // E_H

To copy to clipboard, switch view to plain text mode 

#include "paint.h"
#include <QPainter>
 
 
paint::paint(QWidget *parent)
    : QWidget(parent)
{
 
}
 
void paint::paintEvent(QPaintEvent *e)
{
  Q_UNUSED(e);
  QPainter qp(this);
  drawLines(&qp);
}
 
void paint::drawLines(QPainter *qp)
{QColor color(Qt::red);
 
  qp->setPen(color);
}

#include "paint.h"
#include <QPainter>


paint::paint(QWidget *parent)
    : QWidget(parent)
{

}

void paint::paintEvent(QPaintEvent *e)
{
  Q_UNUSED(e);
  QPainter qp(this);
  drawLines(&qp);
}

void paint::drawLines(QPainter *qp)
{QColor color(Qt::red);

  qp->setPen(color);
}

To copy to clipboard, switch view to plain text mode 

#include "paint.h"
#include <QApplication>
 
int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
 
  paint window;
 
  window.resize(280, 270);
  window.move(300, 300);
  window.setWindowTitle("Lines");
  window.show();
 
  return app.exec();
}

#include "paint.h"
#include <QApplication>

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

  paint window;

  window.resize(280, 270);
  window.move(300, 300);
  window.setWindowTitle("Lines");
  window.show();

  return app.exec();
}

To copy to clipboard, switch view to plain text mode 

[anda_skoa]

What do you mean?
This should bring up an empty window, why do you expect a red one?

Cheers,
_

[rezas1000]

I like the red window.
But the following code does not.

void paint::drawLines(QPainter *qp)
{QColor color(Qt::red);
 
  qp->setPen(color);
}

void paint::drawLines(QPainter *qp)
{QColor color(Qt::red);

  qp->setPen(color);
}

To copy to clipboard, switch view to plain text mode 

[Radek]

Okay, you have set the pen but where are the drawn lines? IMO, the paint::drawLines() needs some updating. If you want a red window, get the rectangle from the event and qp->fillRect() the rectangle by red color.

[rezas1000]

Thank you very much
But,I'm sorry.I do not understand.

[Radek]

Setting the pen tells the painter which pen it should use in subsequent painting but it paints nothing. Your drawLines() takes the pen in a hand and - returns without painting anything. If you want a red rectangle (or lines or something else), you need taking the pen in a hand and painting. Something like this:

void paint::paintEvent(QPaintEvent *e)
{
  QPainter  qp(this);
  QRect     rect(e->rect());
 
  qp.fillRect(rect,Qt::red);
}

void paint::paintEvent(QPaintEvent *e)
{
  QPainter  qp(this);
  QRect     rect(e->rect());

  qp.fillRect(rect,Qt::red);
}

To copy to clipboard, switch view to plain text mode 

and remove the drawLines(). Or, if you plan to use such procedure, pass it the rectangle along with the painter. Also, for better readibility of your code, make the paint:aintEvent() virtual. Yes, I know, it is already virtual because the QWidget:aintEvent() is virtual but specifying what is what allows you to orient in your code better.

[stampede]

Also, for better readibility of your code, make the paint:aintEvent() virtual. Yes, I know, it is already virtual because the QWidget:aintEvent() is virtual but specifying what is what allows you to orient in your code better.

Or use "override" specifier if you are using C++11.

[Nomad_Tech]

Do you mean you want a window with a red background?

I usually find it easiest to give my widgets/windows a custom palette if I just want to change the color only. Something like:

QPalette redWindowPalette;
redWindowPalette.setColor(QPalette::Background, QColor(225,75,75,255));  //set background role to a pale red
setPalette(redWindowPalette);//set our widgets palette to the new red background palette

QPalette redWindowPalette;
redWindowPalette.setColor(QPalette::Background, QColor(225,75,75,255));  //set background role to a pale red
setPalette(redWindowPalette);//set our widgets palette to the new red background palette

To copy to clipboard, switch view to plain text mode