C#中this的用法集锦 C#中this的用法集锦

时间:2021-03-21 人气:0

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this 关键字引用类的当前实例，还可用作扩展方法的第一个参数的修饰符。下面就针对this的四种用法，做简单的总结。

首先，我们分别创建User和VIP两个C#类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
namespace AppConsole
{
 
  /// <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
  {
 
  }
}

this第【1】种用法，索引器

/// <summary>
/// 全局变量
/// </summary>
Dictionary<string, object> dictInfo = null;
 
/// <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; }
}

this第【2】种用法，当做参数传递

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

this第【3】种用法，通过this()调用无参构造函数

/// <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;
}

this第【4】种用法：扩展User类

/// <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));
  }
}

最后，控制台测试

/// <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();
 
}

最终结果示意图

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