请教！怎样让选中的feature闪烁

<img src="images/post/smile/dvbbs/em30.gif" />请教，怎样让选中的feature闪烁，谢谢！！！！！！！！！！

<P>'‖=================================================<BR>'‖功能：闪烁实体<BR>'‖参数：<BR>'‖输出：<BR>'‖=================================================<BR>Private Sub FlashPoint(pDisplay As IScreenDisplay, pGeometry As IGeometry)<BR>  On Error GoTo ErrorHandler</P>
<P>  Dim pMarkerSymbol As ISimpleMarkerSymbol<BR>  Dim pSymbol As ISymbol<BR>  Dim pRGBColor As IRgbColor<BR>  <BR>  Set pRGBColor = New rgbcolor<BR>  pRGBColor.Green = 128<BR>  <BR>  Set pMarkerSymbol = New SimpleMarkerSymbol<BR>  pMarkerSymbol.Style = esriSMSCircle<BR>  pMarkerSymbol.Color = pRGBColor<BR>   <BR>  Set pSymbol = pMarkerSymbol<BR>  pSymbol.ROP2 = esriROPNotXOrPen<BR>  <BR>  pDisplay.SetSymbol pMarkerSymbol<BR>  pDisplay.DrawPoint pGeometry<BR>  Sleep 300<BR>  pDisplay.DrawPoint pGeometry</P>
<P>  Exit Sub<BR>ErrorHandler:<BR>  HandleError False, "FlashPoint " ; c_sModuleFileName ; " " ; GetErrorLineNumberString(Erl), err.Number, err.Source, err.Description, 4<BR>End Sub</P>

选中的feature，用两个不同颜色的FillSymbol，间隔交叉显示，具体用什么接口，自己查帮助吧