Qt/C++ widget inside widget does not appear - c++

Question

I am writing Qt/C++ project and I created my mainwindow.ui in QtDesigner. I placed in mainwindow.ui an empty widget which later I want to extend by putting there my widget written in code. This is my code:
class which extends QWidget
#pragma once
#include <QtGui>
#include <QWidget>
using namespace QtDataVisualization;
class GraphDataCreator : public QWidget
{
Q_OBJECT
public:
GraphDataCreator(QWidget* parent = 0);
~GraphDataCreator();
};
cpp of this class:
#include "GraphDataCreator.h"
GraphDataCreator::GraphDataCreator(QWidget* parent)
: QWidget(parent)
{
this->setStyleSheet("background-color:green;");
}
and the mainwindow class:
#pragma once
#include <QMainWindow>
#include "ui_MainWindow.h"
#include "GraphDataCreator.h"
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
MainWindow(QMainWindow*parent = Q_NULLPTR);
~MainWindow();
private:
Ui::MainWindow ui;
};
cpp of main window class
#include "MainWindow.h"
#include <string>
#include <QtGui>
#include "GraphDataCreator.h"
MainWindow::MainWindow(QMainWindow*parent)
: QMainWindow(parent)
{
ui.setupUi(this);
QGridLayout* layout = new QGridLayout(ui.Chart3DWidget);
GraphDataCreator* chart3D = new GraphDataCreator(ui.Chart3DWidget);
layout->addWidget(chart3D);
QWidget* test_widget = new QWidget;
test_widget->setStyleSheet("background-color: red;");
layout->addWidget(test_widget);
ui.Chart3DWidget->setLayout(layout);
}
I wanted to be the whole widget in ui green, but it didn't appear so I put there test_widget with red background and the result is that it is half nothing/half red. So the green widget excists there but it is not visible. And my question is why the green part is not visible??? And how to solve it?
Of course names of classes are weird because I tried to do something else and this explanation simplifies that problem.
EDIT:
thx #sajas for help! Actually I used that link Why do stylesheets not work when subclassing QWidget and using Q_OBJECT? and I used case 2 written there so I deleted Q_OBJECT macro in GraphDataCreator class and it worked without any other changes. The function for background color of widget I left the same and everything else. The result is as expected half green / half red. Anyway I think I should include macro Q_Object as written in link over there because it is a Qt class, but it does work without. Maybe there is a small bug in Qt??? To sum up if you delete Q_Object macro it works.