On the other hand, I still struggle understanding how to create a custom-reusable-widget, which i defined its own stylesheet, but after it become a child widget, it will lose all the top level styling and only the components style will be applied (es. QPushButton, QLabel ecc..) because Qt erase the top level QWidget stylesheet for optimization purpose, or at least this is what I understand from reading posts

Normally the last set and more specific settings should apply.

See here:

• https://doc.qt.io/qt-6/stylesheet-syntax.html
  • https://doc.qt.io/qt-6/stylesheet-syntax.html#conflict-resolution
  • https://doc.qt.io/qt-6/stylesheet-syntax.html#cascading
  • https://doc.qt.io/qt-6/stylesheet-syntax.html#inheritance

To do so, you need to edit your final project "file.pro" and add the folder's paths where your custom widget live like so

"
inside .pro file
INCLUDEPATH += " insert/path/toyour/customWidgets "
"
After that, you can select "add existing file" directly from the Projects panel
.

On the other hand, I still struggle understanding how to create a custom-reusable-widget, which i defined its own stylesheet, but after it become a child widget, it will lose all the top level styling and only the components style will be applied (es. QPushButton, QLabel ecc..) because Qt erase the top level QWidget stylesheet for optimization purpose, or at least this is what I understand from reading posts

I Tryed removing the "backgroung-color" from the stylesheet of the WindowFrame.ui and replace it with "transparent".
After that I Tryed addign the stylesheet directly to the component and also to the TrackManager.ui targeting the WindowFrame {}

this is the result:

#include "trackmanager.h"
#include "ui_trackmanager.h"

TrackManager::TrackManager(QWidget *parent)
    : QWidget(parent)
    , ui(new Ui::TrackManager)
{
    ui->setupUi(this);

    QString TEMP_USER{"genericmail@gmail.it"};
    QString TEMP_POWER{"Admin"};

    /*  Declaration status bar & title window  */
    m_statusbar = new QStatusBar();
    m_titlebar = new WindowFrame(TEMP_USER, TEMP_POWER, this);
    m_titlebar->setStyleSheet("QWidget { background-color: \"#9b0000\";}");
    connect(m_titlebar, &WindowFrame::maximizedClicked, this, &QWidget::showMaximized);
    connect(m_titlebar, &WindowFrame::minimizedClicked, this, &QWidget::showMinimized);

    QVBoxLayout* window_layout = qobject_cast<QVBoxLayout*>(this->layout());
    window_layout->insertWidget(0, m_titlebar);
    window_layout->insertWidget(2, m_statusbar);
}

QWidget
{
	background-color: "#7e7474";
}


#toolbar_wdg
{
	background-color: "#883d3d";
	border-radius: 12;
}


QToolButton
{
	background-color: white;
	border-radius: 8;
	border: 2 solid transparent;

	outline: 0;
}

QToolButton:checked
{
	background-color: rgb(239, 99, 102);
}

QToolButton:hover
{
	border-color:  rgb(56, 132, 255);
}

WindowFrame QWidget
{
	background-color: red;
}

I was tring to share the code but the page gave me the error of "spam message"

:-1: error: debug/windowframe.o:windowframe.cp:(.rdata$.refptr._ZTV11WindowFrame[.refptr._ZTV11WindowFrame]+0x0): undefined reference to `vtable for WindowFrame'

• Clean everything out of build output directory and rebuild.
• Does your WindowFrame class have/need Q_OBJECT macro?

C:/Qt/Tools/mingw1120_64/bin/../lib/gcc/x86_64-w64-mingw32/11.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: debug/windowframe.o: in function `WindowFrame::on_maximize_tbnt_clicked()':
C:/Qt/Tools/mingw1120_64/bin/../lib/gcc/x86_64-w64-mingw32/11.2.0/../../../../x86_64-w64-mingw32/bin/ld.exe: debug/windowframe.o: in function `WindowFrame::on_minimize_tbtn_clicked()':
collect2.exe: error: ld returned 1 exit status
C:\Users\path\Qt_c++\TrackInspector\windowframe.cpp:50: error: undefined reference to `WindowFrame::showNormalClicked()'
:-1: error: C:\Users\path\Qt_c++\TrackInspector\build\Desktop_Qt_6_7_1_MinGW_64_bit-Debug/../../windowframe.cpp:54: undefined reference to `WindowFrame::maximizedClicked()'
C:\Users\path\Qt_c++\TrackInspector\windowframe.cpp:61: error: undefined reference to `WindowFrame::minimizedClicked()'
:-1: error: debug/windowframe.o:windowframe.cp:(.rdata$.refptr._ZTV11WindowFrame[.refptr._ZTV11WindowFrame]+0x0): undefined reference to `vtable for WindowFrame'
:-1: error: [Makefile.Debug:83: debug/TrackInspector.exe] Error 1

My .pro file look like this now:

QT       += core gui

greaterThan(QT_MAJOR_VERSION, 4): QT += widgets

CONFIG += c++17

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
    main.cpp \
    trackmanager.cpp \
    windowframe.cpp

HEADERS += \
    ../TitleCustomBar/profilebanner.h \
    trackmanager.h
    windowframe.h

FORMS += \
    ../TitleCustomBar/profilebanner.ui \
    ../TitleCustomBar/windowframe.ui \
    trackmanager.ui

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

RESOURCES += \
    resource.qrc

INCLUDEPATH += "C:\Users\path\Qt_c++\TitleCustomBar"

Hi,

if you have multiple and different "title bar" widgets, which you want to show depending on your configuration or user, looking at the Document Viewer example may help.
This project uses different viewer widgets (loaded as Qt plugin library) for each context of the app

• https://doc.qt.io/qt-6/qtdoc-demos-documentviewer-example.html

Try this, when you have multiple title bar widgets, or you simply include the one class in your app like @jsulm said.

INCLUDEPATH += "the path to my CustomTitleBar" to my TrackManager.pro file

This is not enough: you also need the cpp file. Without it you get the error you posted.