在PPT放映时， 画出来的直线屏幕一闪，又没有了,怎么解决

在PPT放映时， 画出来的直线屏幕一闪，又没有了,如何解决
PowerPoint.SlideShowSettings oSettings;
  oSettings=Globals.ThisAddIn.Application.ActivePresentation.SlideShowSettings;  
  oSettings.Run();
  PowerPoint.SlideShowView ssv = Globals.ThisAddIn.Application.SlideShowWindows[1].View;
  if (ssv.PointerType == PowerPoint.PpSlideShowPointerType.ppSlideShowPointerPen)
  {
  ssv.PointerType = PowerPoint.PpSlideShowPointerType.ppSlideShowPointerArrow;
  }
  else
  {
  ssv.PointerType = PowerPoint.PpSlideShowPointerType.ppSlideShowPointerPen;
  ssv.PointerColor.RGB = 123;
  }
  ssv.DrawLine((float)0.0, (float)0.0, (float)150.0, (float)150.0);

  画出来的直线屏幕一闪，又没有了

[解决办法]
http://www.cnblogs.com/dlwang2002/archive/2007/10/29/941000.html