/// <summary>
    /// 用户登录信息存储
    /// </summary>
    public class UserInfo
    { 
        /// <summary>
        /// 登录账号
        /// </summary>
        public static String uid = "";
        /// <summary>
        /// 登录密码
        /// </summary>
        public static String pwd = "";
    }
    /// <summary>
    /// 用户登录类
    /// </summary>
    public class UserLogin
    {
        /// <summary>
        /// 登录方法
        /// </summary>
        /// <param name="uid">账号</param>
        /// <param name="pwd">密码</param>
        public void Login(String uid,String pwd)
        {
            UserInfo.pwd = pwd;
            UserInfo.uid = uid;
        }
    }
    /// <summary>
    /// 数据库访问类
    /// </summary>
    public class UserService
    {
        /// <summary>
        /// 添加信息
        /// </summary>
        /// <param name="mes"></param>
        public void Add(String mes)
        { 
            //获得登录人ID
            String uid = UserInfo.uid;
            //......................剩下的访问数据库内容略
        }
    }