c# - "this"如何在C#中传递

Question

我试图了解“this”如何在 C#-6.0 (VS 2015) 中作为属性传递。

using System;

public class Person
{
    private Person instance;

    public Person()
    {
        instance = this;
    }

    public Person myself
    {
        get { return instance; }
        set { instance = value; }
    }

    public string name = "Eddie";

}

public class Example
{
    public static void Main()
    {
        Person firstPerson = new Person();
        Person secondPerson = firstPerson.myself;

        secondPerson.name = "Bill";
        Console.WriteLine(firstPerson.name);
        Console.WriteLine(secondPerson.name);

        firstPerson.myself = new Person();
        Console.WriteLine(firstPerson.name);
        Console.WriteLine(secondPerson.name);

        Console.ReadLine();
    }
}

我的假设是当行:

Person secondPerson = firstPerson.myself;

运行后，secondPerson 成为对 firstPerson 的引用，因此当我将名称更改为“Bill”时，firstPerson.name 和 secondPerson.name 都是 Bill。但是当我跑的时候

firstPerson.myself = new Person();

我希望 firstPerson.name 和 secondPerson.name 回到“Eddie”，但它仍然是“Bill”。为什么？提前致谢!

Answer 1

您更改了 firstPerson.instance 指向的 Person 实例，但未更改 firstPerson 指向的原始实例。

因此 firstPerson 仍然指向原始的 Person 实例(因此 firstPerson.name 返回第一个实例中设置的值)，而 firstPerson.instance 现在指向一个新的(第二个)Person 实例。

Person firstPerson = new Person();            // instance 1
Person secondPerson = firstPerson.myself;     // myself refers to instance 1

secondPerson.name = "Bill";                   // set name in instance 1
Console.WriteLine(firstPerson.name);          // get name from instance 1
Console.WriteLine(secondPerson.name);         // get name from myself in instance 1
Console.WriteLine(firstPerson.myself.name);   // get name from instance 1 (same as above)

firstPerson.myself = new Person();            // myself refers to instance 2, but firstPerson still refers to instance 1
Console.WriteLine(firstPerson.name);          // still getting name from instance 1
Console.WriteLine(secondPerson.name);         // still getting name from myself in instance 1
Console.WriteLine(firstPerson.myself.name);   // get name from instance 2 (since firstPerson.myself was reassigned)

firstPerson = new Person();                   // firstPerson and firstPerson.myself point to instance 3
Console.WriteLine(firstPerson.name);          // get name from instance 3, which is the default "Eddie"
Console.WriteLine(secondPerson.name);         // still points to instance 1, since that's what it was when it was assigned
Console.WriteLine(firstPerson.myself.name);   // get name from instance 3 (since firstPerson.myself is defaults to the new instance again)