.NET 4.0 中 Lazy 类得简单使用

.NET 4.0 中 Lazy 类让我的 ORM 小框架又向前迈了一步，下面是我做的一个小Demo，来演示它的用法：

UserCompany.cs

    /// <summary>
    /// 用户所在的公司
    /// </summary>
    public class UserCompany
    {
        public int CompanyId { get; set; }

        public string CompanyName { get; set; }

        public string CompanyDescription { get; set; }
    }

UserCompanyService.cs

    public static class UserCompanyService
    {
        private static readonly List<UserCompany> ltCompany = new List<UserCompany>()
        {
            new UserCompany(){ CompanyId = 1, CompanyName = "中国移动", CompanyDescription = "中国移动的相信介绍在这里" },
            new UserCompany(){ CompanyId = 2, CompanyName = "中国联通", CompanyDescription = "中国联通的相信介绍在这里" },
            new UserCompany(){ CompanyId = 3, CompanyName = "中国电信", CompanyDescription = "中国电信的相信介绍在这里" },
        };

        public static List<UserCompany> GetAllCompany()
        {
            return ltCompany;
        }

        public static UserCompany GetCompanyById(int companyId)
        {
            return ltCompany.SingleOrDefault(c => c.CompanyId == companyId);
        }
    }

UserInfo.cs

    /// <summary>
    /// 用户信息
    /// </summary>
    public class UserInfo
    {
        public UserInfo()
        {
            UserCompany_UserCompanyId = new Lazy<UserCompany>(() => UserCompanyService.GetCompanyById(UserCompanyId));
        }

        public int Id { get; set; }

        public string UserName { get; set; }

        public DateTime UserBirthday { get; set; }

        public int UserCompanyId { get; set; }

        public Lazy<UserCompany> UserCompany_UserCompanyId { get; set; }
    }

UserInfoService.cs

    public class UserInfoService
    {
        private static readonly List<UserInfo> ltUserInfo = new List<UserInfo>()
        {
            new UserInfo(){ Id = 1, UserName = "张三", UserCompanyId = 1 },
            new UserInfo(){ Id = 2, UserName = "李四", UserCompanyId = 2 },
            new UserInfo(){ Id = 3, UserName = "王五", UserCompanyId = 1 },
            new UserInfo(){ Id = 4, UserName = "赵六", UserCompanyId = 3 }
        };

        public static List<UserInfo> GetAllUserInfo()
        {
            return ltUserInfo;
        }

        public static UserInfo GetUserInfoById(int userInfoId)
        {
            return ltUserInfo.SingleOrDefault(u => u.Id == userInfoId);
        }
    }

UserInfoManager.cs

    public class UserInfoManager
    {
        public static List<UserInfo> GetAllUserInfo()
        {
            return UserInfoService.GetAllUserInfo();
        }
    }

Program.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Threading;

namespace ConAppLazyload
{
    class Program
    {
        static void Main(string[] args)
        {
            /* 基本 */
            Lazy<string> lzTime = new Lazy<string>(Program.GetCurrentTime);
            Console.WriteLine(lzTime.IsValueCreated);
            Console.WriteLine(lzTime.Value);
            Console.WriteLine(lzTime.IsValueCreated);

            /* 高级 */

            List<UserInfo> ltAllUserInfo = UserInfoManager.GetAllUserInfo();
            foreach (UserInfo userInfo in ltAllUserInfo)
            {
                Console.WriteLine();
                Console.WriteLine(userInfo.Id);
                Console.WriteLine(userInfo.UserName);
                Console.WriteLine(userInfo.UserBirthday);
                Console.WriteLine(userInfo.UserCompanyId);
                Console.WriteLine(userInfo.UserCompany_UserCompanyId.IsValueCreated);
                Console.WriteLine(userInfo.UserCompany_UserCompanyId.Value.CompanyName);
                Console.WriteLine(userInfo.UserCompany_UserCompanyId.IsValueCreated);
                Console.WriteLine();
            }
        }

        static string GetCurrentTime()
        {
            return DateTime.Now.ToString("yyyy-MM-dd");
        }
    }
}

附件下载：http://files.cnblogs.com/Music/CSharp4Lazy.rar

谢谢浏览！

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