C#中this的用法集錦

2020-01-24 01:48:02

字體：大中小

來源：轉載

供稿：網友

this 關鍵字引用類的當前實例，還可用作擴展方法的第一個參數的修飾符。下面就針對this的四種用法，做簡單的總結。

首先，我們分別創建User和VIP兩個C#類

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks; namespace AppConsole{   /// <summary>  /// 普通用戶  /// </summary>  public class User  {    /// <summary>    /// 全局變量    /// </summary>    Dictionary<string, object> dictInfo = null;     /// <summary>    /// 構造器    /// </summary>    public User()    {      dictInfo = new Dictionary<string, object>();    }     /// <summary>    /// 構造函數重載    /// </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】種用法，索引器    /// </summary>    /// <param name="name"></param>    /// <returns></returns>    public object this[string name]    {      get { return dictInfo[name]; }      set { dictInfo[name] = value; }    }      /// <summary>    /// 編號    /// </summary>    public int ID { get; set; }      /// <summary>    /// 用戶名    /// </summary>    public string UserName { get; set; }     /// <summary>    /// this第【2】種用法，當做參數傳遞    /// </summary>    public void Said()    {      new VIP().Say(this);    }   }   /// <summary>  /// 會員  /// </summary>  public class VIP : User  {      /// <summary>    /// 積分    /// </summary>    public int integral { get; set; }     /// <summary>    /// 構造函數    /// </summary>    public VIP()    {      ID = 520;      integral = 1000;    }     /// <summary>    /// this第【3】種用法，通過this()調用無參構造函數    /// </summary>    /// <param name="UserName"></param>    public VIP(string UserName)      : this()    {      this.UserName = UserName;    }     /// <summary>    /// 構造函數重載    /// </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！我的編號是{0}，大家可以叫我{1}！", user.ID, user.UserName));    }   }   /// <summary>  /// 靜態類，來擴展User類  /// </summary>  public static class Helper  {     /// <summary>    /// 第【4】種用法： this擴展User類    /// </summary>    /// <param name="user"></param>    public static void Sing(this User user)    {      Console.WriteLine(string.Format("嗨，大家好！我的編號是{0}，大家可以叫我{1}！", user.ID, user.UserName));    }  }   /// <summary>  /// 特性類：指定特性僅適用于方法和方法的參數  /// </summary>  [System.AttributeUsage(AttributeTargets.Method | AttributeTargets.Parameter)]  public class LCQAttribute : System.Attribute  {   }}

this第【1】種用法，索引器

/// <summary>/// 全局變量/// </summary>Dictionary<string, object> dictInfo = null; /// <summary>/// this，第【1】種用法，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】種用法，當做參數傳遞

/// <summary>/// this第【2】種用法，當做參數傳遞/// </summary>public void Said(){  new VIP().Say(this);}

this第【3】種用法，通過this()調用無參構造函數

/// <summary>/// this第【3】種用法，通過this()調用無參構造函數/// </summary>/// <param name="UserName"></param>public VIP(string UserName)  : this(){  this.UserName = UserName;}

this第【4】種用法：擴展User類

/// <summary>/// 靜態類，來擴展User類/// </summary>public static class Helper{   /// <summary>  /// 第【4】種用法： this擴展User類  /// </summary>  /// <param name="user"></param>  public static void Sing(this User user)  {    Console.WriteLine(string.Format("嗨，大家好！我的編號是{0}，大家可以叫我{1}！", user.ID, user.UserName));  }}

最后，控制臺測試

/// <summary>/// 主程序入口/// </summary>/// <param name="args"></param>static void Main(string[] args){   //0>聲明實體  User user = new User();  user.ID = 1;  user.UserName = "lichaoqiang";   //第【一】種用法:this用作索引器 public object this[string name]{……}  user["UserID"] = 1;  Console.WriteLine("第【一】種用法:this用作索引器");   //第【二】種用法:this用作參數傳遞 user.Say(this);  Console.WriteLine("第【二】種用法:this用作參數傳遞");  user.Said();   //第【三】種用法:this() public VIP:this(){  }  VIP vip = new VIP("yezi");  vip.Said();  Console.WriteLine("第【三】種用法:this()");   //第【四】種用法： this擴展VIP類 public static Sing(this User user){……}  Console.WriteLine("第【四】種用法： this擴展VIP類");  user.Sing();    Console.Read(); }

最終結果示意圖