定义对象为什不可以写到while语句外面。VS2017

        /// <summary>

        /// 绑定产品信息到网络列表

        /// </summary>

        private void BindProduct()

        {

            Pros = new List<ProductClass>();

            SqlDataReader sdr = SqlHelper.Read("SELECT Id,JWD,ProName,ProNum,ProStyle FROM dbo.product");

            while (sdr.Read())

            {

                ProductClass pro = new ProductClass();//为什么不能写到while语句外面

                pro.Id = Convert.ToInt32(sdr["Id"]);

                pro.JWD = sdr["JWD"].ToString();

                pro.ProName = sdr["ProName"].ToString();

                pro.ProNum = sdr["ProNum"].ToString();

                pro.ProStyle = sdr["ProStyle"].ToString();

                Pros.Add(pro);

            }

            sdr.Close();

            dgvProduct.DataSource = Pros;

        }