The sub-object cannot display when i add the Q_OBJECT in my code

ctrkalk

I try to add a object which extend to qwidget to another widget as sub-object.but when i add the "Q_OBJECT" define in to that object,they will disappear and only show the parent qwidget.
that is my code(just for test,which show the basic formation)

main.cpp :the core code

#include <QApplication>
#include <QMainWindow>
#include <QPushButton>
#include <iostream>
#include "code.h"
#include "PGW.h"
using namespace std;

int main(int argc, char* argv[]) {
    QApplication a(argc, argv);
    code c = code();
    c.show();
    return a.exec();

    // RenderPass();
}

codecpp ,which is the parent widget

#include "code.h"
#include <QPushButton>
#include <iostream>
#include <QDebug>
#include <QVulkanWindow>
#include <QVulkanInstance>
#include "PGW.h"
//#include "render.h"
using namespace std;
code::code() {
    this->setGeometry(0,0,1000,1000);
    m* w = new m(this);
    w->setGeometry(0, 0, 100, 100);
    w->setStyleSheet("background-color: red;");
    w->show();
}
code::~code()
{
}

PGW.cpp,which is the sub-object

#include "PGW.h"
m::m(QWidget* p) : QWidget(p) {
    
}
m::~m() {}

and this is the header files:
code.h:

#include "code.h"
#include <QPushButton>
#include <iostream>
#include <QDebug>
#include <QVulkanWindow>
#include <QVulkanInstance>
#include "PGW.h"
//#include "render.h"
using namespace std;
code::code() {
    this->setGeometry(0,0,1000,1000);
    m* w = new m(this);
    w->setGeometry(0, 0, 100, 100);
    w->setStyleSheet("background-color: red;");
    w->show();
}
code::~code()
{
}

PGW.h:

#include <QWidget>
class m : public QWidget {
   Q_OBJECT //remove this can make this widget show
public:
     
   m(QWidget* p= nullptr);
    ~m();
};
``

ChrisW67

code::code() {
    this->setGeometry(0,0,1000,1000);
    m* w = new m(this);
    w->setGeometry(0, 0, 100, 100);
    w->setStyleSheet("background-color: red;");
    w->show();
}

Is w supposed to be shown on top of the code widget, laid out inside the code widget, or completely independent of the code widget?

ctrkalk

it not independent,and today i discover that if the m extend to qpushbutton or qlable,all is current(althougt i add the define of "Q_OBJECT“).but if i change it to qwidget,is cannot finded in parent widget

Bonnie

@ctrkalk Then I know the reason, it is not that it doesn't show, but the stylesheet doesn't work, so the widget is totally transparent.
There're already quite a lot posts in the forum asking about subclassed QWidget's stylesheet not working.
It is also documented:

If you subclass from QWidget, you need to provide a paintEvent for your custom QWidget as below:
...

But this is the first time I know that a subclassed QWidget without Q_OBJECT would have stylesheet working :)

BTW, the simplest solution for this kind of problem (if you don't want to reimplement paintEvent) is to subclass QFrame instead of QWidget, or using palette instead of stylesheet.