c# - Drawn shape in Picturebox doesn't clear -

i trying show train moves on map .so let me explain method ,i draw map on picturebox map,and trains on picturebox train,i put train picturebox on map picturebox .

more details:https://stackoverflow.com/a/9158849/2538037

so use 2 function here :

 public void drawmap()         {              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);                      graph.drawstring(objstationrepository.findby(i => i.id == t.stationid).first().name, pictureboxmetromap.font, brushes.white, t.xlocation +40, t.ylocation +50);                  }             }              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);                      graph.drawstring(objstationrepository.findby(i => i.id == t.stationid).first().name, pictureboxmetromap.font, brushes.white, t.xlocation - 50, t.ylocation - 30);                 }             }              graph.drawlines(pline, lstpointleft.toarray());             graph.drawlines(pline, lstpointright.toarray());             pictureboxmetromap.image = map;           } 

this function draws map ,and function draws trains on picturebox:

 public void drawonlinetrain()         {             var graph = graphics.fromimage(map);              if (onlinetrainlist.count > 0)             {                  foreach (onlinetrain t in onlinetrainlist.tolist())                 {                    // graph.dispose();                     rectangle recttrainstate = new rectangle(t.xtrainlocation.value - 3,                                                              t.ytrainlocation.value - 3,                                                              7, 7);                     graph.fillrectangle(redbrush, recttrainstate);                 }             }             pictureboxonlinetrain.image = map;        } 

so use thread update train picturebox ,i call thread in form_load :

 private void frmmain_load(object sender, eventargs e)         {             pictureboxonlinetrain.parent = pictureboxmetromap;             map= new bitmap(pictureboxmetromap.size.width, pictureboxmetromap.size.height);             updatelistbox = new updatelistboxdelegate(this.updatestatus);             // initialise , start worker thread             workerthread = new thread(new threadstart(this.getonlinetrain));             workerthread.start(); } 

so in thread start method gets location of online train:

  public void getonlinetrain()         {                    while(true)             {                 onlinetrainrepository objonlinetrainrepository = new onlinetrainrepository();                 onlinetrainlist = objonlinetrainrepository.getall().tolist();                 objonlinetrainrepository = null;                 invoke(updatelistbox);              }          } 

here start updatelistbox draw train:

 private void updatestatus()         {              foreach (onlinetrain onlinetrain in onlinetrainlist.tolist())             {                lstlog.items.add("train id=" + onlinetrain.trainid + " | current x position=" + onlinetrain.xtrainlocation + " | current y position=" + onlinetrain.ytrainlocation);               pictureboxonlinetrain.image = null;                  drawonlinetrain();             }           } 

as can see here show movement have clear old location of trains ,and using :

pictureboxonlinetrain.image = null; 

but doesn't work ,and every rectangle remain on screen ?!!!

best regards

1. address problem directly

• you never clear bitmap! note drawing on top of there when using graphics.fromimage
• you use 1 , same bitmap object drawing. (in combination previous point) have entire "scene" in map time - no need have several pictureboxes in case!
• be careful: if picturebox refresehes while you're drawing, unfinished state visible! manipulating image shown.

2. do

• render 1 buffer (you using bitmap fine, maybe consider using bufferedgraphics)
• render control whenever (or it's paint event fires) instead of using picturebox