单例模式应用

再一个类库中创建一个Factory,这个Factory用于调用其他类，从而调用其他类中的方法

DALFactory中：

 public class DALFactory
    {
　　　　 private static DALFactory _instance;
　　　　　//单例模式
        public static DALFactory Instance 
　　　　　{ 
　　　　　　get 
　　　　　　{ 
　　　　　　　　if(_instance==null)
　　　　　　　　{
　　　　　　　　　　_instance=new DALFactory();
　　　　　　　　}
　　　　　　　　return _instance;
　　　　　　} 
　　　　　}
        private DALFactory() { }
        public UsersDAL UsersDAL
        {
            get { return new UsersDAL(); }
        }
    }

普通类：

 public class UsersDAL
    {
        //public static UsersDAL Instance { get { return new UsersDAL(); } }
        //private UsersDAL() { }

        #region 用户登录
        /// <summary>
        /// 用户登录
        /// </summary>
        /// <param name="username">用户名</param>
        /// <param name="password">用户密码</param>
        /// <returns>该用户</returns>
        public Users UserLogin(string username, string password)
        {
            Users user = null;
            using (EF.schoolshopEntities content = new EF.schoolshopEntities())
            {
                var entity = content.SS_Users.FirstOrDefault(u => u.UserName == username && u.Password == password &&u.DelFlag==0);
                if (entity != null)
                {
                    user = CreatUser(user, entity);
                }
            }
            return user;
        }

        /// <summary>
        /// 根据uid获取用户
        /// </summary>
        /// <param name="uid">用户ID</param>
        /// <returns>该用户</returns>
        public Users GetUserByUID(int uid)
        {
            Users user = null;
            using (EF.schoolshopEntities content = new EF.schoolshopEntities())
            {
                var entity = content.SS_Users.FirstOrDefault(u => u.UID == uid);
                if (entity != null)
                {
                    user = CreatUser(user, entity);
                }
            }
            return user;
        }

        /// <summary>
        /// 实体转化成模型
        /// </summary>
        /// <param name="user"></param>
        /// <param name="entity"></param>
        /// <returns></returns>
        private Users CreatUser(Users user, EF.SS_Users entity)
        {
            user = new Users() 
            {
                UID = entity.UID,
                UserName = entity.UserName,
                Password = entity.Password,
                NickName = entity.NickName,
                Mobile = entity.Mobile,
                Email = entity.Email,
                Gender = entity.Gender,
                Address = entity.Address,
                LastLoginTime = entity.LastLoginTime,
                Birthday = entity.Birthday,
                RegistTime = entity.RegistTime,
            };
            return user;
        }

        #endregion

    }

BLLFactory中：

   public class BLLFactory
    {
        public static BLLFactory Instance { get { return new BLLFactory(); } }
        private BLLFactory() { }

        public UsersBLL UsersBLL
        {
            get { return new UsersBLL(); }
        }
    }

普通类：

 public class UsersBLL 
    {
        //public static UsersBLL Instance { get { return new UsersBLL(); } }
        //private UsersBLL() { }

        #region 用户登录
        /// <summary>
        /// 判断用户登录
        /// </summary>
        /// <param name="username">用户名</param>
        /// <param name="password">用户密码</param>
        /// <returns>该用户</returns>
        public Users UserLogin(string username, string password)
        {
            Users user = DALFactory.Instance.UsersDAL.UserLogin(username, password); //UsersDAL.Instance.UserLogin(username, password);
            return user;
        }
          /// <summary>
        /// 根据uid获取用户
        /// </summary>
        /// <param name="uid">用户ID</param>
        /// <returns>该用户</returns>
        public Users GetUserByUID(int uid)
        {
            Users user = DALFactory.Instance.UsersDAL.GetUserByUID(uid); //UsersDAL.Instance.GetUserByUID(uid);
            return user;
        }

        #endregion
    }

如果点的太多可以：

        private UsersDAL _userDao;

        public UsersBLL()
        {
            _userDao = DALFactory.Instance.UsersDAL;
        }