QMainWindow and custom widget doesn't show

[Peppy]

I have problems with this code:
(MainWindow.cpp)

MainWindow::MainWindow(QWidget * parent) : QMainWindow(parent)
{
      QWidget * widget = new QWidget;
  QVBoxLayout * layout = new QVBoxLayout;
    MyWidget * w = new MyWidget;
    w->setRectBackgroundColor(255,255,255,255);
    w->setHeight(110);
    w->show();
    layout->addWidget(w,0);
    widget->setLayout(layout);
     setCentralWidget(widget);
}

MainWindow::MainWindow(QWidget * parent) : QMainWindow(parent)
{
      QWidget * widget = new QWidget;
  QVBoxLayout * layout = new QVBoxLayout;
    MyWidget * w = new MyWidget;
    w->setRectBackgroundColor(255,255,255,255);
    w->setHeight(110);
    w->show();
    layout->addWidget(w,0);
    widget->setLayout(layout);
     setCentralWidget(widget);
}

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(MyWidget.h)

class MyWidget : public QWidget
{
Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);
            ~MyWidget(void){ };
        void setHeight(int height);
        void setRectBackgroundColor(int r,int g, int b, int a);
        void setRectBackgroundColor(const QColor &bgColor);
protected:
     virtual void paintEvent(QPaintEvent * e);
private:
     QColor rectBgColor;
        int rectHeight;
};

class MyWidget : public QWidget
{
Q_OBJECT
public:
    explicit MyWidget(QWidget *parent = 0);
            ~MyWidget(void){ };
        void setHeight(int height);
        void setRectBackgroundColor(int r,int g, int b, int a);
        void setRectBackgroundColor(const QColor &bgColor);
protected:
     virtual void paintEvent(QPaintEvent * e);
private:
     QColor rectBgColor;
        int rectHeight;
};

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(MyWidget.cpp)

MyWidget::MyWidget(QWidget *parent) : QWidget(parent)
{
    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
}
void MyWidget::setRectBackgroundColor(const QColor &bgColor)
{
  rectBgColor = bgColor;
}
void MyWidget::setRectBackgroundColor(int r, int g, int b, int a)
{
  rectBgColor = QColor(r,g,b,a);
}
void MyWidget::setHeight(int height)
{
 rectHeight = height;
}
void MyWidget::paintEvent(QPaintEvent *e)
{
  QPainter painter;
  painter.begin(this);
  painter.setPen(Qt::NoPen);
  painter.setBrush(QBrush(rectBgColor,Qt::SolidPattern));
  painter.drawRect(QRect(0,0,rect().width()+1,rectHeight));
  painter.end();
}

MyWidget::MyWidget(QWidget *parent) : QWidget(parent)
{
    setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Fixed);
}
void MyWidget::setRectBackgroundColor(const QColor &bgColor)
{
  rectBgColor = bgColor;
}
void MyWidget::setRectBackgroundColor(int r, int g, int b, int a)
{
  rectBgColor = QColor(r,g,b,a);
}
void MyWidget::setHeight(int height)
{
 rectHeight = height;
}
void MyWidget::paintEvent(QPaintEvent *e)
{
  QPainter painter;
  painter.begin(this);
  painter.setPen(Qt::NoPen);
  painter.setBrush(QBrush(rectBgColor,Qt::SolidPattern));
  painter.drawRect(QRect(0,0,rect().width()+1,rectHeight));
  painter.end();
}

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Problem is: In main window it doesn't show any white rectangle... I think is problem with body of MainWindow constructor, because on QWidget window it is working. I am so unhappy with this problem.

[kiss-o-matic]

How are you adding your widget to the QMainWindow, and how are you calling the main window? Basically, show your main().

[Peppy]

main.cpp:

int main(int argv, char * argc[])
{
   QApplication a(argv,argc);
   MainWindow mW;
   mW.show();
  return a.exec();
}

int main(int argv, char * argc[])
{
   QApplication a(argv,argc);
   MainWindow mW;
   mW.show();
  return a.exec();
}

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[numbat]

The documentation says:

When implementing a new widget, it is almost always useful to reimplement sizeHint() to provide a reasonable default size for the widget and to set the correct size policy with setSizePolicy().

By default, composite widgets which do not provide a size hint will be sized according to the space requirements of their child widgets.

and

QSizePolicy::Fixed - The QWidget::sizeHint() is the only acceptable alternative, so the widget can never grow or shrink (e.g. the vertical direction of a push button).

In short, you need to provide a sizeHint implementation.

[Peppy]

Done, still nothing...

[soxs060389]

Did you try to add other custom widgets to your MainWindow as central widget? Was that successfull?

[Peppy]

No, I didn't.

[numbat]

Done, still nothing...

Works for me with your code. Maybe you could upload a zip of your project. My implementation of sizeHint follows:

QSize MyWidget::sizeHint() const
{
   return QSize(100, 110);
}

QSize MyWidget::sizeHint() const
{
   return QSize(100, 110);
}

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[LoginFailed]

Cause the MainWindow has its own Layout and in its center has a Widget.I think first you should use the function setCenterWidget() to add an Widget as you defined(like QGroupBox),and setLayout in this Widget , then set Widgets which you want to show in you MainWindow in this Layout.

[Peppy]

my sizeHint():

QSize MyWidget::sizeHint()
{
  return QSize(rect().width()+1, rectHeight );
}

QSize MyWidget::sizeHint()
{
  return QSize(rect().width()+1, rectHeight );
}

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