QBoxLayout with QMainWindow vs QWidget

[Vyivrain]

Hello.I'd like to ask about the thing that is happening ,when I use QHBoxLayout with QMainWindow and with QWidget.I'm trying to change window title style, by connecting 2 widgets.
This what's happening: Under QWidget
1.jpg
Here's the code for class under QWidget:
TitleBar.h

#ifndef MYTITLEBAR_H
#define MYTITLEBAR_H
 
#include <QMainWindow>
#include <QMouseEvent>
#include <QToolButton>
#include <QStyle>
#include <QLabel>
#include <QHBoxLayout>
#include <QPixmap>
 
class MyTitleBar : public QWidget
{
public:
    MyTitleBar( QWidget* parent );
public slots:
    void showSmall();
    void showMaxRestore();
 
protected:
    void mousePressEvent( QMouseEvent* me );
    void mouseMoveEvent( QMouseEvent* me );
 
private:
    QToolButton* minimize;
    QToolButton* maximize;
    QToolButton* close;
    QToolButton* custom;
    QPixmap restorePix, maxPix, closePix, minPix, customPix;
    bool maxNormal;
    QPoint startPos;
    QPoint clickPos;
};
 
#endif // MYTITLEBAR_H

#ifndef MYTITLEBAR_H
#define MYTITLEBAR_H

#include <QMainWindow>
#include <QMouseEvent>
#include <QToolButton>
#include <QStyle>
#include <QLabel>
#include <QHBoxLayout>
#include <QPixmap>

class MyTitleBar : public QWidget
{
public:
    MyTitleBar( QWidget* parent );
public slots:
    void showSmall();
    void showMaxRestore();

protected:
    void mousePressEvent( QMouseEvent* me );
    void mouseMoveEvent( QMouseEvent* me );

private:
    QToolButton* minimize;
    QToolButton* maximize;
    QToolButton* close;
    QToolButton* custom;
    QPixmap restorePix, maxPix, closePix, minPix, customPix;
    bool maxNormal;
    QPoint startPos;
    QPoint clickPos;
};

#endif // MYTITLEBAR_H

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TitleBar.cpp

#include "mytitlebar.h"
 
MyTitleBar::MyTitleBar( QWidget* parent )
{
    this->setWindowFlags( Qt::FramelessWindowHint );
 
    minimize = new QToolButton(this);
    maximize = new QToolButton(this);
    close = new QToolButton(this);
    custom = new QToolButton(this);
 
    closePix.load( "close.png" );
    close->setIcon( closePix );
 
    maxPix.load( "maximize.png" );
    maximize->setIcon( maxPix );
 
    minPix.load( "minimize.png" );
    minimize->setIcon( minPix );
 
    customPix.load( "custom_icon.png" );
    custom->setIcon( customPix );
 
    QLabel* label = new QLabel(this);
    label->setText( "Custom Window" );
 
    QHBoxLayout* HBox = new QHBoxLayout( this );
 
    HBox->addWidget( custom );
    HBox->addWidget( label );
    HBox->addWidget( minimize );
    HBox->addWidget( maximize );
    HBox->addWidget( close );
 
 
 
}
 
void MyTitleBar::showSmall()
{
 
}
 
void MyTitleBar::showMaxRestore()
{
 
}
 
void MyTitleBar::mousePressEvent(QMouseEvent *me)
{
 
}
 
void MyTitleBar::mouseMoveEvent(QMouseEvent *me)
{
 
}

#include "mytitlebar.h"

MyTitleBar::MyTitleBar( QWidget* parent )
{
    this->setWindowFlags( Qt::FramelessWindowHint );

    minimize = new QToolButton(this);
    maximize = new QToolButton(this);
    close = new QToolButton(this);
    custom = new QToolButton(this);

    closePix.load( "close.png" );
    close->setIcon( closePix );

    maxPix.load( "maximize.png" );
    maximize->setIcon( maxPix );

    minPix.load( "minimize.png" );
    minimize->setIcon( minPix );

    customPix.load( "custom_icon.png" );
    custom->setIcon( customPix );

    QLabel* label = new QLabel(this);
    label->setText( "Custom Window" );

    QHBoxLayout* HBox = new QHBoxLayout( this );

    HBox->addWidget( custom );
    HBox->addWidget( label );
    HBox->addWidget( minimize );
    HBox->addWidget( maximize );
    HBox->addWidget( close );



}

void MyTitleBar::showSmall()
{

}

void MyTitleBar::showMaxRestore()
{

}

void MyTitleBar::mousePressEvent(QMouseEvent *me)
{

}

void MyTitleBar::mouseMoveEvent(QMouseEvent *me)
{

}

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But under QMainWindow, happens something like this:
2.jpg

The code is exactly the same as for QWidget, but I've changed the parent and inheritance to QMainWindow.And returning to the question why is this happening and how I can fix this? In the main window it's just intancing the class and move it to the right place, that it'd look like a window title bar and is the same as for QWidget and QMainWindow. I need to use QMainWindow as parent, because the main window is inheritance of QMainWindow.

[anda_skoa]

QMainWindow already has a layout.

The content area of a main window is called the central widget, see QMainWindow::setCentralWidget().

So if your code works in a widget, keep it there and set this widget as the central widget or add it to the actual central widget
Or use a QToolBar and add it to the main window.

Cheers,
_