尝试通过Gridview更新/删除一行时，为什么删除了XML文件中的所有数据？

I have an Editable Gridview, which functions off of an XML file. When I attempt to Update/Delete a row via the Gridiview, all the data in the XML file is then deleted. When I insert a new row, the pending data is replaced w/ the new row. Could I please get some direction as to what I'm doing wrong? I provided my xml file and the four methods used for editing the GridView. I have an Editable Gridview, which functions of