private void setUpModel()
        {
            model = new GameModel();
            ScenarioComponent scenario    = new ScenarioComponent(20, 20); // 20 x 20 Gameworld.
            Building          obstruction = new Building();

            // Add grass cells at each cell.
            ZRTSModel.Map map = scenario.GetGameWorld().GetMap();
            for (int i = 0; i < map.GetWidth(); i++)
            {
                for (int j = 0; j < map.GetHeight(); j++)
                {
                    CellComponent cell = new CellComponent();
                    cell.AddChild(new Sand());
                    cell.X = i;
                    cell.Y = j;

                    if (i >= 2 && i <= 10 && j >= 2 && j <= 10)
                    {
                        cell.AddEntity(obstruction);
                    }

                    if (i >= 15 && i <= 18 && j >= 15 && j <= 18)
                    {
                        cell.AddEntity(obstruction);
                    }
                    if (i == 16 && j == 16)
                    {
                        cell.RemoveEntity(obstruction);
                    }

                    map.AddChild(cell);
                }
            }
            model.AddChild(scenario);
        }
 public void Undo()
 {
     player.GetUnitList().RemoveChild(unit);
     cell.RemoveEntity(unit);
 }