定义一个反射dll

 public class DemoTest
    {

        public string Test(DataSet ds)
        {
            IWorkbook workbook = new HSSFWorkbook();
            string fileName =  DateTime.Now.ToString("yyyyMMddHHmmss") + ".xls";
            ISheet sheet = workbook.CreateSheet("Sheet1");
            IRow row;
            ICell cell;
            int rowIndex = 0;
            int cellInex = 0; 
            row = sheet.CreateRow(rowIndex++);
            foreach(DataColumn dc in ds.Tables[0].Columns)
            {
                cell=row.CreateCell(cellInex++);
                cell.SetCellValue(dc.ColumnName); 
            }
            foreach(DataRow dr in ds.Tables[0].Rows)
            {
                row = sheet.CreateRow(rowIndex++);
                cellInex = 0;
                foreach (DataColumn dc in ds.Tables[0].Columns)
                {
                    cell = row.CreateCell(cellInex++);
                    cell.SetCellValue(dr[dc.ColumnName].ToString());
                }
            }

            var uploadPath = Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "upload");
            fileName = Path.Combine(uploadPath, fileName);
            using (FileStream fs = new FileStream(fileName, FileMode.Create, FileAccess.Write))
            {
                workbook.Write(fs);
            }
            return fileName;
        }

        public static int Sum(int a,int b)
        {
            return a + b;
        }
    }

引用反射dll

   // 获取rocky.dll的文件路径
            string foder = Server.MapPath(string.Format("~/{0}", "upload"));
            Assembly ass = Assembly.LoadFrom(string.Format("{0}/lib/demo.dll",foder));
            // 获取该dll中命名空间RockyNameSpace中Study类
            Type type = ass.GetType("Demo.DemoTest");
            // 实例化该类
            object obj = Activator.CreateInstance(type);
            // 获取该类中的方法StudyMath
            MethodInfo mStudyMath = type.GetMethod("Test"); 
            //静态调用
           var s= type.GetMethod("Sum", BindingFlags.Public | BindingFlags.Static).Invoke(null, new object[] { 1,4});

            DataSet ds = new DataSet();
            DataTable dt = new DataTable();
            dt.Columns.Add("A1");
            dt.Columns.Add("A2");
            dt.Columns.Add("A3");
            dt.Columns.Add("A4");
            DataRow dr;
            for(var i = 0; i < 10; i++)
            {
                dr = dt.NewRow();
                dr[0] = "A" + i.ToString();
                dr[1] = "B" + i.ToString();
                dr[2] = "C" + i.ToString();
                dr[3] = "D" + i.ToString();
                dt.Rows.Add(dr);
            }
            ds.Tables.Add(dt);
            // 使用方法
           var path= mStudyMath.Invoke(obj, new object[] { ds }) ;