QGridLayout addWidget(CustomWidget) is not working - c++

Question

I'm using the QGridLayout in my code, and want to add my custom widget to gridlayout, it's not working with addWidget(CustomWidget*).
This is runing on Windows10 with Visual Studio 2013 and Qt5.6.3.
// *.h
class MainWindow : public QMainWindow {
Q_OBJECT
public:
MainWindow(QWidget *parent = Q_NULLPTR);
private:
Ui::MainWindow ui;
};
class CustomWidget : public QWidget {
Q_OBJECT
public:
CustomWidget(QWidget *parent = Q_NULLPTR) : QWidget(parent) {}
~CustomWidget() {}
};
// *.cpp
// when i use CustomWidget
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
ui.setupUi(this);
QWidget *grid = new QWidget(this);
grid->setStyleSheet("background:pink;");
QGridLayout *layout = new QGridLayout(grid);
layout->setMargin(0);
layout->setSpacing(0);
grid->setLayout(layout);
grid->setGeometry(500, 150, 240, 180);
// following code is not working, when run this program,
// i can only see the 'grid' widget with pink background
CustomWidget *w = new CustomWidget(grid);
w->setStyleSheet("background:red;");
layout->addWidget(w, 0, 0);
}
// but if i use QWidget
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent) {
ui.setupUi(this);
QWidget *grid = new QWidget(this);
grid->setStyleSheet("background:pink;");
QGridLayout *layout = new QGridLayout(grid);
layout->setMargin(0);
layout->setSpacing(0);
grid->setLayout(layout);
grid->setGeometry(500, 150, 240, 180);
// following code is working, when run this program,
// i can see the 'w' widget with red background
QWidget *w = new QWidget(grid);
w->setStyleSheet("background:red;");
layout->addWidget(w, 0, 0);
}

Answer 1

As it is said in the Qt's stylesheets reference, applying CSS styles to custom widgets inherited from QWidget requires reimplementing paintEvent() in that way:
void CustomWidget::paintEvent(QPaintEvent *)
{
QStyleOption opt;
opt.init(this);
QPainter p(this);
style()->drawPrimitive(QStyle::PE_Widget, &opt, &p, this);
}
Although for what it says in the documentation, without doing it your custom widgets will support only the background, background-clip and background-origin properties, for what might be a bug.
You can read about it here: Qt Stylesheets reference in the section "List of Stylable Widgets" -> QWidget.