首先先拉一个DropDownList控件

  <asp:DropDownList ID="ddl_Class" runat="server"  CssClass="form-control"></asp:DropDownList>

后台代码编写：

editId = Convert.ToInt32(Request.QueryString["Id"]);

 //2.1定义查询SQL
                string sql = "SELECT * FROM dbo.Student WHERE Id=@Id";
                //2.2定义参数化查询的参数
                SqlParameter[] pams = {
                    new SqlParameter("@Id",editId)
                };
                //2.3通过DbHelper来执行查询语句获取学员的信息
                using (SqlDataReader reader = DbHelper.ExecuteReader(sql, pams))
                {
                    //先判断reader里面有没有行数据
                    if (reader.HasRows)
                    {
                        //向下移动一次游标
                        if (reader.Read())
                        {
                            //开始读取数据 放在对象中
                            StudentModel model = new StudentModel()
                            {
                                Age = Convert.ToInt32(reader["Age"]),
                                ClassId = Convert.ToInt32(reader["ClassId"]),
                                Email = reader["Email"].ToString(),
                                Id = Convert.ToInt32(reader["Id"]),
                                Mobile = reader["Mobile"].ToString(),
                                Name = reader["Name"].ToString()
                            };
                            //2.4将学员的信息绑定到页面上
                            txt_Name.Text = model.Name;
                            txt_Age.Text = model.Age.ToString();
                            txt_Email.Text = model.Email;
                            txt_Mobile.Text = model.Mobile;

                            //3.绑定班级的下拉框
                            //3.1读取出班级信息
                            //1.定义查询SQL语句
                            string sqlCalss = "SELECT * FROM dbo.Class";
                            //2.通过DbHelper来查询数据
                            DataTable dt = DbHelper.ExecuteTable(sqlCalss);
                            //3.进行下拉框的数据绑定
                            ddl_Class.DataSource = dt;
                            ddl_Class.DataTextField = "ClassName";
                            ddl_Class.DataValueField = "Id";
                            ddl_Class.DataBind();
                            //3.3使下拉框的选中项指向当前学员的班级ID
                            ddl_Class.SelectedValue = model.ClassId.ToString();

                        }
                    }
                }