#include <QtWidgets/QApplication>
#include <QtWidgets/QMainWindow>
#include <QtWidgets/QDockWidget>
#include <QtWidgets/QListWidget>
#include <QFile>
#include <Windows.h>

class MainWindow : public QMainWindow
{
    void closeEvent(QCloseEvent* ce)
    {
        // Save
        QByteArray state = saveState();
        QByteArray geom = saveGeometry();
        QFile file("workspace.bin");
        file.open(QIODevice::WriteOnly);
        QDataStream out(&file);
        out << state;
        out << geom;
        file.close();
    }
};

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

    MainWindow mw;

    QDockWidget* dock = new QDockWidget("dock", &mw);
    dock->setObjectName("dock");

    dock->setAllowedAreas(Qt::LeftDockWidgetArea | Qt::RightDockWidgetArea);
    QListWidget* customerList = new QListWidget(dock);
    customerList->addItems(QStringList() << "John Doe, Harmony Enterprises, 12 Lakeside, Ambleton"
                                         << "Jane Doe, Memorabilia, 23 Watersedge, Beaton"
                                         << "Tammy Shea, Tiblanka, 38 Sea Views, Carlton"
                                         << "Tim Sheen, Caraba Gifts, 48 Ocean Way, Deal"
                                         << "Sol Harvey, Chicos Coffee, 53 New Springs, Eccleston"
                                         << "Sally Hobart, Tiroli Tea, 67 Long River, Fedula");
    dock->setWidget(customerList);

    mw.addDockWidget(Qt::DockWidgetArea::RightDockWidgetArea, dock);

    QWidget* central = new QWidget(&mw);
    central->setStyleSheet("background-color:red");
    mw.setCentralWidget(central);

    // Restore if exists
    {
        QFile file("workspace.bin");
        file.open(QIODevice::ReadOnly);
        QDataStream in(&file);
        QByteArray state;
        QByteArray geom;
        in >> state;
        in >> geom;

        mw.restoreGeometry(geom);
        mw.show();
        mw.restoreState(state);

        file.close();
    }

    a.exec();

    return 0;
}