this的作用--转载

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

namespace AppConsole
{
    class Program
    {
        /// <summary>
        /// 主程序入口
        /// </summary>
        /// <param name="args"></param>
        static void Main(string[] args)
        {

            //0>声明实体
            User user = new User();
            user.ID = 1;
            user.UserName = "lichaoqiang";

            //第【一】种用法:this用作索引器 public object this[string name]{……}
            user["UserID"] = 1;
            Console.WriteLine("第【一】种用法:this用作索引器");

            //第【二】种用法:this用作参数传递 user.Say(this);
            Console.WriteLine("第【二】种用法:this用作参数传递");
            user.Said();

            //第【三】种用法:this() public VIP:this(){   }
            VIP vip = new VIP("yezi");
            vip.Said();
            Console.WriteLine("第【三】种用法:this()");

            //第【四】种用法： this扩展VIP类 public static Sing(this User user){……}
            Console.WriteLine("第【四】种用法： this扩展VIP类");
            user.Sing();

            Console.Read();

        }

    }

    /// <summary>
    /// 普通用户
    /// </summary>
    public class User
    {
        /// <summary>
        /// 全局变量
        /// </summary>
        Dictionary<string, object> dictInfo = null;

        /// <summary>
        /// 构造器
        /// </summary>
        public User()
        {
            dictInfo = new Dictionary<string, object>();
        }

        /// <summary>
        /// 构造函数重载
        /// </summary>
        /// <param name="UserID"></param>
        /// <param name="UserName"></param>
        public User(int UserID, string UserName)
        {
            this.UserName = UserName;
            this.ID = UserID;
        }

        /// <summary>
        /// this，第【1】种用法，索引器
        /// </summary>
        /// <param name="name"></param>
        /// <returns></returns>
        public object this[string name]
        {
            get { return dictInfo[name]; }
            set { dictInfo[name] = value; }
        }

        /// <summary>
        /// 编号
        /// </summary>
        public int ID { get; set; }

        /// <summary>
        /// 用户名
        /// </summary>
        public string UserName { get; set; }

        /// <summary>
        /// this第【2】种用法，当做参数传递
        /// </summary>
        public void Said()
        {
            new VIP().Say(this);
        }

    }

    /// <summary>
    /// 会员
    /// </summary>
    public class VIP : User
    {

        /// <summary>
        /// 积分
        /// </summary>
        public int integral { get; set; }

        /// <summary>
        /// 构造函数
        /// </summary>
        public VIP()
        {
            ID = 520;
            integral = 1000;
        }

        /// <summary>
        /// this第【3】种用法，通过this()调用无参构造函数
        /// </summary>
        /// <param name="UserName"></param>
        public VIP(string UserName)
            : this()
        {
            this.UserName = UserName;
        }

        /// <summary>
        /// 构造函数重载
        /// </summary>
        /// <param name="UserID"></param>
        /// <param name="UserName"></param>
        public VIP(int UserID, string UserName)
            : base(UserID, UserName)
        {

        }

        /// <summary>
        ///Say方法
        /// </summary>
        /// <param name="user"></param>
        public void Say([LCQAttribute] User user)
        {
            Console.WriteLine(string.Format("嗨，大家好！我的编号是{0}，大家可以叫我{1}！", user.ID, user.UserName));
        }

    }

    /// <summary>
    /// 静态类，来扩展User类
    /// </summary>
    public static class Helper
    {

        /// <summary>
        /// 第【4】种用法： this扩展User类
        /// </summary>
        /// <param name="user"></param>
        public static void Sing(this User user)
        {
            Console.WriteLine(string.Format("嗨，大家好！我的编号是{0}，大家可以叫我{1}！", user.ID, user.UserName));
        }
    }

    /// <summary>
    /// 特性类：指定特性仅适用于方法和方法的参数
    /// </summary>
    [System.AttributeUsage(AttributeTargets.Method | AttributeTargets.Parameter)]
    public class LCQAttribute : System.Attribute
    {

    }
}