Question

我注意到如果你在一个类中有一个私有成员，你可以通过引用它的名称在类方法中访问它。您无需说this.memberName，只需memberName即可。那么在成员访问的上下文中this关键字是可选的吗？

当你想澄清范围时，我确实看到它很有用 - 当你有两个同名的变量时。访问会员时是否还有其他理由使用它？

Answer 1

是的，它是可选的。您必须使用它的唯一时间是当您有一个隐藏成员变量的局部变量，或者您想要引用indexed property (aka indexer)时。

Answer 2

您可以选择在实例成员（例如实例方法或属性）中使用this实例成员访问，因为无论何时调用实例方法this（引用当前对象）都会自动传入作为一个不可见的参数。

您无法在静态成员中使用this来访问实例成员...就像您无法在静态方法中使用this.x或this.y（甚至是简单的x和y）或x或y是实例成员的属性。这是因为静态成员调用中未定义this。静态成员属于整个类......它不知道this指的是哪个实例。这是因为当您调用静态方法或属性时，调用的格式为ClassName.MethodName();，因此静态方法不知道对象this将引用什么。

this也不是可选的（必须使用）作为扩展方法的参数列表中的第一个修饰符。实际上this是将静态方法标识为扩展方法的原因。现在this将第一个参数标识为扩展方法正在运行的实例。

    using System;



    class Class_name
    {


        static  string static_variable="static";

        string instance_variable="instance";


        static void Main()
        {

            Class_name object_name = new Class_name();

            Console.WriteLine("Printing out instance and static variables from within Main() body :");

            Console.WriteLine(object_name.instance_variable);
            Console.WriteLine(Class_name.static_variable);

            /* Note that we cannot say either of the following :

                    object_name.static_variable 
                    Class_name.instance_variable


            */

            Console.WriteLine();




            // now lets call the static and instance methods

            object_name.Instance_method(); // Now this is the key call which 
            // passes "this" as an invisible parameter 
            // to the Instance_method. "this" refers to  
            //  object_name


            Class_name.Static_method();//  "this" is NOT passed to Static_method() because now 
            // the call is made on Class_name ... so there is nothing
            // to be represented by "this"


            Console.ReadLine();

        }



        void Instance_method()
        { 

            // here we receive "this" as an invisible parameter referring 
            // to the object on which  Instance_method is called (i.e. object_name)...
            // ... see the Main() method for comments at the call site. 


            Console.Write("Instace method called ... " +
                            "prints out instance variable twice, with and without 'this': ");

            // the following two calls mean exactly the same.

            Console.Write(this.instance_variable);
            Console.WriteLine (instance_variable);



            // one little additional point is that static members are 
            // accessible from within instance members


            Console.WriteLine();

            Console.Write("static variables can also be accessed from within Instance_method: ");
            Console.WriteLine(static_variable);

            Console.WriteLine();
            Console.WriteLine();




        }


        static void Static_method()
        {

            // See the Main() method body for the call Class_name.Static_method()
            // Notice that this method is called on Class_name and not object_name
            // which means that there is no invisibly passed-in "this" parameter available
            // in this method. 

            // we can also not access the instance_variable in this method 
            // as instance variables are always part of some object. This method
            // is not called on any object, its called on Class_name.

            // Console.WriteLine(instance_variable); // Compiler error

            Console.WriteLine("Static method called ... prints out static variable: ");
            Console.WriteLine(static_variable);




        }






    }

Answer 3

是的，'这个'是隐含的。它有时可以帮助澄清。而且调用方法也需要引用当前的类。

Answer 4

当你调用当前类的成员时，“this”几乎总是可选的。

但是，它用于其他目的，例如将当前类实例作为参数传递或将属性，字段或变量设置为当前实例。

您必须使用它来调用方法的唯一情况是您调用扩展方法时：

class AClass {
    void CallIt() {
        Test();                     //not valid
        this.Test();                //valid 
    }
}
static class AnExtension {
    public static void Test(this AClass source) {

    }
}

当访问C＃中的成员时，`this`关键字是否可选？

4 个答案: