Canvas does not allow drawing

Question

procedure TCameraForm.Timer1Timer(Sender: TObject);
var
 Can:TCanvas;
begin
  Can := TCanvas.Create;
  Can.Handle := GetDC(Cap);
  Can.Pen.Style := psDot;
  Can.Brush.Style := bsClear;
  Can.Pen.Color := RGB(255,255,255);
  Can.Rectangle(X,Y,X + 150,Y + 170);
 // can.Destroy;
end;procedure TCameraForm.FormClose(Sender: TObject; var Action: TCloseAction);
begin
  timer1.Enabled:=false;
end;procedure TCameraForm.FormShow(Sender: TObject);
begin
timer1.Enabled:=true;
end;procedure TCameraForm.FormHide(Sender: TObject);
begin
  timer1.Enabled:=false;
end;
程序运行正常，但是运行几分钟后就报告错误了：canvas does not allow drawing
高手帮忙呀，学校招生报名人多呀，出这个问题了，我是菜鸟呀，只有20分了

Answer 1

画的太快了，画完以后最好Sleep一下

Answer 2

procedure   TCameraForm.Timer1Timer(Sender:   TObject);
var
  Can:TCanvas;
begin
    Can   :=   TCanvas.Create;
    Can.Handle   :=   GetDC(Cap);
    Can.Pen.Style   :=   psDot;
    Can.Brush.Style   :=   bsClear;
    Can.Pen.Color   :=   RGB(255,255,255);
    Can.Rectangle(X,Y,X   +   150,Y   +   170);
    ReleaseDC(Handle,Can.Handle);   //********************
    Can.Destroy;                    //********************
end;