试图用C＃读取Excel文件文件流，我得到数字而不是文本

I'm trying to use DocumentFormat.OpenXml to read an uploaded Excel file. When I get the file (HttpPosteFileWrapper) I'm simply trying to read the cells and write them to a text string. (Later I will do more, but I'm just trying to get used to OpenXml right now.)I'm trying to use DocumentFormat.OpenXml to rea