掌上报销，费用报销单保存时将发票金额汇总到指定字段

【应用场景】

掌上报销，费用报销单保存时将发票金额汇总到指定字段

【实现步骤】

<1>编写python插件，代码示例如下。 

#引入clr运行库

import clr

#添加对cloud插件开发的常用组件的引用

clr.AddReference('System')

clr.AddReference('System.Data')

clr.AddReference('Kingdee.BOS')

clr.AddReference('Kingdee.BOS.Core')

clr.AddReference('Kingdee.BOS.App')

clr.AddReference('Kingdee.BOS.ServiceHelper')

#导入cloud基础库中的常用实体对象（分命名空间导入，不会递归导入）

from Kingdee.BOS import *

from Kingdee.BOS.Core import *

from Kingdee.BOS.Core.Bill import *

from Kingdee.BOS.Core.DynamicForm.PlugIn import *

from Kingdee.BOS.Core.DynamicForm.PlugIn.ControlModel import *

from System import *

from System.Data import *

from Kingdee.BOS.App.Data import *

from System.Collections.Generic import List

from Kingdee.BOS.ServiceHelper import *

#重载插件事件，在保存前汇总发票金额

def BeforeDoOperation(e):

       billObj = this.Model.DataObject;

       if str(e.Operation.FormOperation.Operation.T