首先把架子搭好，如下图

然后一层一层的写，先写模型层,例如：

  public class User
        {
            private string userId;

            public string UserId
            {
                get { return userId; }
                set { userId = value; }
            }
            private string userPwd;

            public string UserPwd
            {
                get { return userPwd; }
                set { userPwd = value; }
            }
            private string userName;

            public string UserName
            {
                get { return userName; }
                set { userName = value; }
            }
            private string userSex;

            public string UserSex
            {
                get { return userSex; }
                set { userSex = value; }
            }
            private string userTel;

            public string UserTel
            {
                get { return userTel; }
                set { userTel = value; }
            }
            private string userAddress;

            public string UserAddress
            {
                get { return userAddress; }
                set { userAddress = value; }
            }
            private string userEmail;

            public string UserEmail
            {
                get { return userEmail; }
                set { userEmail = value; }
            }
            private string userImg;

            public string UserImg
            {
                get { return userImg; }
                set { userImg = value; }
            }
        }

然后就是数据链路层，例如：

public class User_DAL
    {  public object CheckLogin(User user, string right)
        {
            string sqlText;
            if (right == "管理员")
            {
                sqlText = "select userPwd from user_tb where userId=@userId";
            }
            else if (right == "部门经理")
            {
                sqlText = "select empPwd from Employee_tb where empId=@userId and empType='部门经理'";
            }
            else if (right == "CR员工")
            {
                sqlText = "select empPwd from Employee_tb where empId=@userId and empType='CR员工'";
            }
            else if (right == "司机")
            {
                sqlText = "select empPwd from Employee_tb where empId=@userId and empType='司机'";
            }
            else if (right == "操作员工")
            {
                sqlText = "select empPwd from Employee_tb where empId=@userId and empType='操作员工'";
            }
            else
            {
                sqlText = "select cusPwd from Customer_tb where cusId=@userId ";
            }
            SqlParameter[] paras = new SqlParameter[1]
            {
                new SqlParameter("userId",user.UserId)
            };
            object obj = SqlLink.GetScaler(sqlText, paras);
            return obj;
        }

｝

然后就是业务逻辑层；例如：

 public class User_BLL
    {
        User_DAL userdal = new User_DAL();
        public int CheckLogin(User user, string right)
        {
            object obj = userdal.CheckLogin(user, right);
            int result = -1;
            if (obj == null)
            {
                result = 0; //用户不存在
            }
            else if (obj.ToString().Trim() == user.UserPwd)
            {
                result = 1;//正确
            }
            else if (obj.ToString().Trim() != user.UserPwd)
            {
                result = 2;//密码错误
            }
            else
            {
                result = 3; //系统错误
            }
            return result;
        }
    }

最后是表示层；例如：

 

  protected void BtnLogin_Click(object sender, EventArgs e)
    {
        try
        {
            //验证登录
            if (txtUserId.Text == "" || txtUserPwd.Text == "")
            {
                Response.Write("");
                return;
            }
            string userId = txtUserId.Text.Trim();
            string userPwd = txtUserPwd.Text.Trim();
            string right = cobRight.Text.Trim();
            user.UserId= userId.Trim();
            user.UserPwd = userPwd.Trim();
            int i =userbll.CheckLogin(user, right);
            if (i == 0)
            {
                Response.Write("");
            }
            else if (i == 1)
            {
                Session["userId"] = txtUserId.Text;
                Session["userPwd"] = txtUserPwd.Text;
                Server.Transfer("Index.aspx");
            }
            else if (i == 2)
            {
                Response.Write("");
            }
            else if (i == 3)
            {
                Response.Write("");
            }

        }
        catch (Exception ex)
        {
            Response.Write(ex.Message);
        }

表示层只写了方法，因为需要据具体需要更改名称。如有需要，敬请留言，有求必应。