通过引用传递变量

Question

如果我有这个class:

public class Foo
{
    Boo a;
    public Foo (ref Boo  b)
    {
        a=b;
    }
}

是 a 将成为对 b 的引用，还是 a 将复制 ref b 指向的值？如果它复制值，我如何使 a 引用 b 和 b 引用参数引用？（像 Java 那样）

Answer 1

Is a going to be a reference to b, or a is going to copy the value which ref b points to ?

这取决于：

如果Boo是引用类型，如下图，a调用后会指向同一个实例

public class Boo
{
    public int Number { get; set; }
}

如果 Boo 是值类型，如下所示，a 将是 ref b 指向的内容的成员副本。

public struct Boo
{
    public int Number { get; set; }
}

Answer 2

请参考以下例子：

    public class Foo
    {
        public string Name { get; set; }
    }

    public class Bar
    {
        public Foo MyFoo { get; set; }

        public Bar(Foo paramFoo)
        {
            this.MyFoo = paramFoo;
        }
    }

这个序列：

        Foo f = new Foo();
        f.Name = "First Foo";

        System.Diagnostics.Debug.WriteLine(f.Name);

        Bar b = new Bar(f);

        System.Diagnostics.Debug.WriteLine(b.MyFoo.Name);

        b.MyFoo.Name = "Renaming Bar Name";

        System.Diagnostics.Debug.WriteLine(f.Name);
        System.Diagnostics.Debug.WriteLine(b.MyFoo.Name);

输出将是：

First Foo
First Foo
Renaming Bar Name
Renaming Bar Name

在这种情况下，我们将 f 引用传递给 Bar ctor，因此 f 和 MyFoo 都指向相同的内存地址，但它们是不同的变量。这意味着，如果我们执行以下操作

        b.MyFoo = new Foo();
        b.MyFoo.Name = "Yet another foo";

        System.Diagnostics.Debug.WriteLine(f.Name);
        System.Diagnostics.Debug.WriteLine(b.MyFoo.Name);

输出将是

Renaming Bar Name
Yet another foo

要更改此行为，您应该使用 ref 关键字，以便将指针发送到该变量。

Answer 3

正常传递引用类型和使用ref关键字肯定是有区别的。

下面的代码应该有解释，请仔细阅读评论：

class Class6
{
    static void Main(string[] args)
    {
        Boo b = new Boo { BooMember = 5 };
        Console.WriteLine(b.BooMember);

        Foo f = new Foo(b);
        // b is unaffected by the method code which is making new object
        Console.WriteLine(b.BooMember);

        Foo g = new Foo(ref b);
        // b started pointing to new memory location (changed in the method code)
        Console.WriteLine(b.BooMember);
    }
}

public class Foo
{
    Boo a;
    public Foo(Boo b)
    {
        a = b;

        // b is just a reference, and actually is a copy of reference passed,
        // so making it point to new object, dosn't affect actual object , check in calling code
        b = new Boo();
    }

    public Foo(ref Boo b)
    {
        a = b;

        // b is just a reference, but actual reference itself is copied,
        // so making it point to new object would make the calling code object reference to point 
        // to new object. check in the calling code.
        b = new Boo();
    }
}

public class Boo
{
    public int BooMember { get; set; }
}

通过引用传递变量

Passing variables by reference

c#

reference