C # usage of this

C # usage of this

This article summarizes several usage of this in C #. I believe it will be useful, but how many have you used? The following are my summary of the usage of this. You are welcome to refer to the usage and related code.

This keyword references the current instance of the class and can also be used as the modifier of the first parameter of the extension method. The following is a brief summary of the four usage methods of this.

First, we create two C # classes: User and VIP.

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Using System; Using System. Collections. Generic; Using System. Linq; Using System. Text; Using System. Threading. Tasks;   Namespace AppConsole {   /// <Summary> /// Common user /// </Summary> Public class User { /// <Summary> /// Global variable /// </Summary> Dictionary <string, object> dictInfo = null;   /// <Summary> /// Constructor /// </Summary> Public User () { DictInfo = new Dictionary <string, object> (); }   /// <Summary> /// Overload the constructor /// </Summary> /// <Param name = "UserID"> </param> /// <Param name = "UserName"> </param> Public User (int UserID, string UserName) { This. UserName = UserName; This. ID = UserID; }   /// <Summary> /// This, [1] usage, Indexer /// </Summary> /// <Param name = "name"> </param> /// <Returns> </returns> Public object this [string name] { Get {return dictInfo [name];} Set {dictInfo [name] = value ;} }     /// <Summary> /// No. /// </Summary> Public int ID {get; set ;}     /// <Summary> /// User Name /// </Summary> Public string UserName {get; set ;}   /// <Summary> /// This parameter is used as a parameter. /// </Summary> Public void Said () { New VIP (). Say (this ); }   }   /// <Summary> /// Member /// </Summary> Public class VIP: User {     /// <Summary> /// Points /// </Summary> Public int integral {get; set ;}   /// <Summary> /// Constructor /// </Summary> Public VIP () { ID = 520; Integral = 1000; }   /// <Summary> /// This is the [3] usage. this () is used to call a non-argument constructor. /// </Summary> /// <Param name = "UserName"> </param> Public VIP (string UserName) : This () { This. UserName = UserName; }   /// <Summary> /// Overload the constructor /// </Summary> /// <Param name = "UserID"> </param> /// <Param name = "UserName"> </param> Public VIP (int UserID, string UserName) : Base (UserID, UserName) {   }   /// <Summary> /// Say Method /// </Summary> /// <Param name = "user"> </param> Public void Say ([LCQAttribute] User user) { Console. WriteLine (string. Format ("Hi, everyone! My ID is {0}. You can call me {1 }! ", User. ID, user. UserName )); }   }   /// <Summary> /// Static class to extend the User class /// </Summary> Public static class Helper {   /// <Summary> /// Method [4]: this extends the User class /// </Summary> /// <Param name = "user"> </param> Public static void Sing (this User user) { Console. WriteLine (string. Format ("Hi, everyone! My ID is {0}. You can call me {1 }! ", User. ID, user. UserName )); } }   /// <Summary> /// Feature class: specifies that a feature is only applicable to parameters of methods and methods. /// </Summary> [System. AttributeUsage (AttributeTargets. Method | AttributeTargets. Parameter)] Public class LCQAttribute: System. Attribute {   } }

This [1] usage, Indexer

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/// <Summary> /// Global variable /// </Summary> Dictionary <string, object> dictInfo = null;   /// <Summary> /// This, [1] usage, Indexer /// </Summary> /// <Param name = "name"> </param> /// <Returns> </returns> Public object this [string name] { Get {return dictInfo [name];} Set {dictInfo [name] = value ;} }

This parameter is used as a parameter.

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/// <Summary> /// This parameter is used as a parameter. /// </Summary> Public void Said () { New VIP (). Say (this ); }

This [3] method, which calls a non-argument constructor through this ()

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/// <Summary> /// This is the [3] usage. this () is used to call a non-argument constructor. /// </Summary> /// <Param name = "UserName"> </param> Public VIP (string UserName) : This () { This. UserName = UserName; }

This [4] usage: extends the User class

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/// <Summary> /// Static class to extend the User class /// </Summary> Public static class Helper {   /// <Summary> /// Method [4]: this extends the User class /// </Summary> /// <Param name = "user"> </param> Public static void Sing (this User user) { Console. WriteLine (string. Format ("Hi, everyone! My ID is {0}. You can call me {1 }! ", User. ID, user. UserName )); } }

Finally, the console Test

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/// <Summary> /// Main program entry /// </Summary> /// <Param name = "args"> </param> Static void Main (string [] args) {   // 0> declare an object User user = new User (); User. ID = 1; User. UserName = "lichaoqiang ";   // [1] usage: this is used as the index public object this [string name] {…} User ["UserID"] = 1; Console. WriteLine ("[1] usage: this is used as the indexer ");   // [2] usage: this is used as the parameter to pass user. Say (this ); Console. WriteLine ("[2] usage: this is used for parameter transfer "); User. Said ();   // [3] usage: this () public VIP: this (){} VIP vip = new VIP ("yezi "); Vip. Said (); Console. WriteLine ("[3] usage: this ()");   // [4] usage: this extends the VIP class public static Sing (this User user ){......} Console. WriteLine ("[4] usage: this extends the VIP class "); User. Sing ();     Console. Read ();   }

Final Result

The above is all the content of this article. I hope you will like it.