#include <QApplication>
#include <QWindow>
#include <QHBoxLayout>
#include <QWidget>
#include <QPushButton>
#include <QMouseEvent>

class customWidget : public QWidget
{
    public:
        customWidget() : QWidget(nullptr) {}
        ~customWidget() override {}
    protected:
        void mousePressEvent(QMouseEvent* event) override
        {
            if (event->button() == Qt::LeftButton && rect().contains(event->pos()))
            {
                windowHandle()->startSystemMove();
                event->accept();
            }
            else
            {
                return QWidget::mousePressEvent(event);
            }
        }
};
class customWidget2 : public QWidget
{
    public:
        customWidget2() : QWidget(nullptr)
        {
            //this can changed to Qt::FramelessWindowHint
            setWindowFlags(Qt::CustomizeWindowHint);
            //
            QHBoxLayout asdfdd;
            setLayout(&asdfdd);
            QPushButton* asdf {new QPushButton};
            asdf->setText("where is window animation?");
            asdfdd.addWidget(asdf);
            QObject::connect(asdf, &QPushButton::clicked, [this] ()
            {
                Qt::WindowStates Local_WindowState {windowState()};
                if (Local_WindowState & Qt::WindowMaximized)
                {
                    showNormal();
                }
                else if (Local_WindowState == Qt::WindowMinimized || Local_WindowState == Qt::WindowNoState)
                {
                    showMaximized();
                }
            });
        }
        ~customWidget2() override {}
    protected:
        void mousePressEvent(QMouseEvent* event) override
        {
            if (event->button() == Qt::LeftButton && rect().contains(event->pos()))
            {
                windowHandle()->startSystemMove();
                event->accept();
            }
            else
            {
                return QWidget::mousePressEvent(event);
            }
        }
    private:
        bool m_Maximized {false};
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    //1
    customWidget w;
    w.resize(800, 600);
    QHBoxLayout asdfdd;
    w.setLayout(&asdfdd);
    QPushButton* asdf {new QPushButton};
    asdf->setText("asdfffwqq");
    asdfdd.addWidget(asdf);
    w.show();
    //2
    customWidget2 w2;
    w2.resize(400, 300);
    w2.show();
    return a.exec();
}