c# - 传递给未更新的类变量

Question

这听起来应该是一个非常基本的问题，但我还没有找到答案(即使我知道肯定有很多)，我想我的谷歌搜索技能很差，或者我不知道要搜索什么为了。

我有这个代码:

using System;

public class Program
{   
    public static void Main()
    {
        var service = new Service();

        service.Execute();
    }
}

public class Service
{
    private int _foo;

    public void Execute()
    {
        _foo = 1;

        var bar = new Bar(_foo);

        _foo = 2;

        bar.WriteLine();
    }
}

public class Bar
{
    private readonly int _foo;

    public Bar(int foo)
    {
        _foo = foo;
    }

    public void WriteLine()
    {
        Console.WriteLine(_foo);
    }
}

我怎样才能让它打印 2 ? (基本上是 Bar之后的新值已经初始化了)

我尝试使用 ref但没有运气。

Answer 1

您尝试做的事情对 value type 没有意义

Value types and reference types are the two main categories of C# types. A variable of a value type contains an instance of the type. This differs from a variable of a reference type, which contains a reference to an instance of the type. By default, on assignment, passing an argument to a method, or returning a method result, variable values are copied. In the case of value-type variables, the corresponding type instances are copied.

通常，您会将其创建为属性并进行相应设置

给定

public class Bar 
{

     public Bar(int foo) => Foo = foo;

     public int Foo {get;set;}

     public void WriteLine() => Console.WriteLine(Foo);

     ...

用法

public void Execute()
{

    var bar = new Bar(1);

    // set the property instead
    bar.Foo = 2;

    bar.WriteLine();

    ...