#include <QApplication>
#include <QtWidgets/QGridLayout>
#include <QtWidgets/QHeaderView>
#include <QtWidgets/QLabel>
#include <QtWidgets/QPushButton>
#include <QtWidgets/QVBoxLayout>
#include <QtWidgets/QWidget>


class FrameLessWidget  : public QWidget
{
public:
    FrameLessWidget(QWidget* parent = 0)
        : QWidget(parent)
        , value(0)
    {
        // Part 1
        setWindowFlags(windowFlags() | Qt::FramelessWindowHint);

        setupUi(this);

        downButton->setText("Down");
        upButton->setText("Up");
        label->setText("---");
        exitButton->setText("Exit");

        connect(upButton, &QPushButton::clicked, this, &FrameLessWidget::increase);
        connect(downButton, &QPushButton::clicked, this, &FrameLessWidget::decrease);
        connect(exitButton, &QPushButton::clicked, []() { qApp->exit(); });
    }

    void setupUi(QWidget* parent) {

        parent->resize(400, 300);

        QVBoxLayout* verticalLayout = new QVBoxLayout(parent);

         // Part 2
        verticalLayout->setContentsMargins(0, 0, 0, 0); // Don't work! no PaintEvents?
        //verticalLayout->setContentsMargins(1, 0, 0, 0); // works!

        QWidget* widget = new QWidget(parent);
        QGridLayout* gridLayout = new QGridLayout(widget);

        downButton = new QPushButton(widget);
        gridLayout->addWidget(downButton, 1, 1, 1, 1);

        label = new QLabel(widget);
        gridLayout->addWidget(label, 0, 0, 1, 1);

        upButton = new QPushButton(widget);
        gridLayout->addWidget(upButton, 0, 1, 1, 1);

        exitButton = new QPushButton(widget);
        gridLayout->addWidget(exitButton, 2, 1, 1, 1);


        verticalLayout->addWidget(widget);
    }

    void decrease() {
        value++;
        label->setText(QString::number(value));
    }

    void increase() {
        value--;
        label->setText(QString::number(value));
    }

private: 
    QPushButton* downButton;
    QPushButton* upButton;
    QLabel*      label;
    QPushButton* exitButton;
    int value;
};


int main(int argc, char* argv[]) {

    QApplication a(argc, argv);

    // Part 3
    a.setAttribute(Qt::AA_NativeWindows);

    FrameLessWidget w;
    w.show();

    return a.exec();
}