交换参考的最佳方法是什么？

Question

What is the best way to exchange references in C#?

Why my static method Exchange doesn't work? But the code in Main works.

class  Person
{    
    public Person(int money)
    {
        Money = money;
    }
    public  int Money { get; set; }
    public static void Exchange(Person p1, Person p2)
    {
        Person newPerson = p1;
        p1 = p2;
        p2 = newPerson;
    }
   public object Clone()
    {
        return new Person( Money);
    }
}
 class Program
{     
    static void Main(string[] args)
    {
        Person p1 = new Person(100);
        Person p2=new Person(200);
        Person newPerson = p1;
        p1 = p2;
        p2 = newPerson;
        Console.WriteLine(p1.Money);
        Console.WriteLine(p2.Money);
        Console.ReadKey();
    }
}

Answer 1

You need the ref keyword:

public static void Exchange(ref Person p1, ref Person p2)

called thusly:

Person.Exchange(ref person1, ref person2);

The reason is that without ref , p1 and p2 are copies of the reference . That's not to say they are copies of the object, but copies of the reference to that object.

See the docs on the ref keyword for more information.

Answer 2

That's because in C# both value and reference types are passed by value ie copy is passed.We need to tell explicitly where we need to pass them by reference.

For reference types a copy of reference is passed. So inside your method swapping them does not affect the original object reference out side the calling method, because the variables outside the calling method have different copy of reference than of those inside the method though they both point to the same object and changing the state from any of them will affect the object.

As @John pointed use ref to pass the references by reference for that.