// 将string 转换成 list
JavaScriptSerializer serialize = new JavaScriptSerializer();
List<DetailContext> List_DetailContext = serialize.Deserialize<List<DetailContext>>(oitem["DetailContext"].SafeToString());
List<XlsxData> _list_XlsxData = new List<XlsxData>();
// 将 list 转换成 string
JavaScriptSerializer serializer = new JavaScriptSerializer();
string json = serializer.Serialize(_list_XlsxData);