清除图片框上绘制的矩形以显示移动

我尝试在我的应用程序中模拟火车运动，所以我使用以下代码创建火车地图:

 public void DrawMap()
        {
            Bitmap map = new Bitmap(pictureBoxMetroMap.Size.Width, pictureBoxMetroMap.Size.Height);
            var graph = Graphics.FromImage(map);
            List<Point> lstPointLeft = new List<Point>();
            foreach (var t in lstSensorLeft)
            {
                Point objPoint = new Point(t.XLocation, t.YLocation);
                lstPointLeft.Add(objPoint);
                Rectangle rectSens = new Rectangle(t.XLocation, t.YLocation, 3, 3);
                try
                {
                    graph.FillRectangle(whiteBrush, rectSens);
                }
                catch (Exception ea)
                {
                }
                if (t.StationId != null)
                {
                    Rectangle rectEhsansq = new Rectangle(t.XLocation - 6, t.YLocation - 6, 12, 12);
                    graph.FillRectangle(blueBrush, rectEhsansq);
                    Label ObjLable = new Label();
                    ObjLable.ForeColor = Color.Transparent;
                    ObjLable.Location = new Point(t.XLocation+40, t.YLocation +50);
                    ObjLable.Text = ObjStationRepository.FindBy(i => i.Id == t.StationId).First().Name;
                    ObjLable.BackColor = Color.Transparent;
                    ObjLable.Width = 70;
                    pictureBoxMetroMap.Controls.Add(ObjLable);
                }
            }
            List<Point> lstPointRight = new List<Point>();
            foreach (var t in lstSensorRight)
            {
                Point objPoint = new Point(t.XLocation + 30, t.YLocation + 30);
                lstPointRight.Add(objPoint);
                Rectangle rectSens = new Rectangle(t.XLocation + 30, t.YLocation + 30, 3, 3);
                graph.FillRectangle(whiteBrush, rectSens);
                if (t.StationId != null)
                {
                    Rectangle rectPosition = new Rectangle(t.XLocation + 24, t.YLocation + 24, 12, 12);
                    graph.FillRectangle(blueBrush, rectPosition);
                    Label ObjLable = new Label();
                    ObjLable.ForeColor = Color.Transparent;
                    ObjLable.Location = new Point(t.XLocation - 50, t.YLocation - 30);
                    ObjLable.Text = ObjStationRepository.FindBy(i => i.Id == t.StationId).First().Name;
                    ObjLable.BackColor = Color.Transparent;
                    ObjLable.Width = 70;
                    pictureBoxMetroMap.Controls.Add(ObjLable);
                }
            }
            graph.DrawLines(pLine, lstPointLeft.ToArray());
            graph.DrawLines(pLine, lstPointRight.ToArray());
            pictureBoxMetroMap.Image = map;
           // ShowOnlineTrain();
            //Thread newThread = new Thread(new ThreadStart(ShowOnlineTrain));
            //newThread.Start();
        }

所以你可以看到DramMap绘制我的火车地图，我调用这个函数在page_load我的应用程序，你可以看到这里:

private void frmMain_Load(object sender, EventArgs e)
    {
        UpdateListBox = new UpdateListBoxDelegate(this.UpdateStatus);
        // Initialise and start worker thread
        workerThread = new Thread(new ThreadStart(this.ShowOnlineTrain));
        workerThread.Start();
        DrawMap();
    }

所以你可以看到上面我调用我的函数，我在我的 pagload 创建一个线程，所以线程做一个重要的操作，它调用函数ShowOnlineTrain，这个函数获取在线列车的位置，我应该在我的地图上显示这些列车:

List<OnlineTrain> OnlineTrainList = new List<OnlineTrain>();
        public void ShowOnlineTrain()
        {
            OnlineTrainRepository objOnlineTrainRepository = new OnlineTrainRepository();

           while(true)
            {
                OnlineTrainList = objOnlineTrainRepository.GetAll().ToList();
                    Invoke(UpdateListBox);
            }

           }
  private void UpdateStatus()
        {
            lstLog.Items.Add("Train Id=" + OnlineTrainList.First().TrainId + " | Current x position=" + OnlineTrainList.First().XTrainLocation + " | Current y position=" + OnlineTrainList.First().YTrainLocation);
        }

这个函数获取在线列车的位置。所以OnlineTrainList **有在线列车的位置(即x和y和trainId)。所以我必须在我的地图上显示火车。我调用我的图片框的**Paint事件:

  private void pictureBoxMetroMap_Paint(object sender, PaintEventArgs e)
        {
            if (OnlineTrainList.Count > 0)
            {
                foreach (OnlineTrain t in OnlineTrainList)
                {
                    var g = pictureBoxMetroMap.CreateGraphics();
                    Rectangle rectTrainState = new Rectangle(t.XTrainLocation.Value - 3,
                                                             t.YTrainLocation.Value - 3,
                                                             7, 7);
                    g.FillRectangle(RedBrush, rectTrainState);
                }
            }
        }

它得到**OnlineTrainList **的所有位置并绘制它们，但我在这里有一个大问题，我需要显示我的火车的运动，我应该清除我的火车的旧位置，但我不知道我该怎么做??我的火车的所有位置都画在我的画框上!!你知道吗?