silverlight 弹窗定位到线的方法

graphic.Symbol = LayoutRoot.Resources["CustomAnimatedRedLineSymbol"] as ESRI.ArcGIS.Client.Symbols.Symbol;
                                ESRI.ArcGIS.Client.Geometry.Polyline pl = graphic.Geometry as ESRI.ArcGIS.Client.Geometry.Polyline;
                                ESRI.ArcGIS.Client.Geometry.PointCollection mpcl = pl.Paths[pl.Paths.Count / 2] as ESRI.ArcGIS.Client.Geometry.PointCollection;
                                mp = mpcl[mpcl.Count/2] as ESRI.ArcGIS.Client.Geometry.MapPoint;
                                CurrentMap.ZoomTo(displayExtent);
                                ElementLayer.SetEnvelope(Infowindow, mp.Extent);