ArcGISFeature.AddAttachmentAsync出错

我在用arcgis runtime for .net 100的ArcGISFeature.AddAttachmentAsync功能j时出错,错误信息为"System.InvalidOperationException: Cannot call this method in this context: Unable to edit attachments.", 请问对空间点要素图层及发布出来的featurelayer服务需要什么条件才能上传附件?