图形符号无法序列化为 JSON:图形符号无法序列化为 JSON

图形符号无法序列化为 JSON:图形符号无法序列化为 JSON
   在 ESRI.ArcGIS.Client.Runtime.NativeGraphicsLayer.GetSymbolJson(Graphic graphic)
   在 ESRI.ArcGIS.Client.Runtime.NativeGraphicsLayer.SerializeGraphic(Graphic graphic, Geometry displayGeometry, BinaryWriter output)
   在 ESRI.ArcGIS.Client.Runtime.NativeGraphicsLayer.<>c__DisplayClass6.<AddGraphics>b__5(BinaryWriter w)
   在 ESRI.ArcGIS.Client.Utils.BinaryWriterExtensions.Write(Action`1 writeAction)
   在 ESRI.ArcGIS.Client.Runtime.NativeGraphicsLayer.AddGraphics(IEnumerable`1 graphicGeometryPairs)
   在 ESRI.ArcGIS.Client.Runtime.NativeGraphicsLayer.layer_GraphicCollectionChanged(Object sender, IEnumerable`1 oldItems, IEnumerable`1 newItems)
   在 ESRI.ArcGIS.Client.GraphicsLayer.Graphics_CollectionChanged(Object sender, NotifyCollectionChangedEventArgs e)
   在 System.Collections.ObjectModel.ObservableCollection`1.OnCollectionChanged(NotifyCollectionChangedEventArgs e)
   在 System.Collections.ObjectModel.ObservableCollection`1.InsertItem(Int32 index, T item)
   在 ESRI.ArcGIS.Client.GraphicCollection.InsertItem(Int32 index, Graphic item)
   在 System.Collections.ObjectModel.Collection`1.Add(T item)
---------------------------------------------------------------
使用自定义点状符号模板设置symbol时（参考例子），报错，不知道该怎么解决？