还有一个代码示例可以展示这一点:

void Main()
{


    int k = 0;
    TestPlain(k);
    Console.WriteLine("TestPlain:" + k);

    TestRef(ref k);
    Console.WriteLine("TestRef:" + k);

    string t = "test";

    TestObjPlain(t);
    Console.WriteLine("TestObjPlain:" +t);

    TestObjRef(ref t);
    Console.WriteLine("TestObjRef:" + t);
}

public static void TestPlain(int i)
{
    i = 5;
}

public static void TestRef(ref int i)
{
    i = 5;
}

public static void TestObjPlain(string s)
{
    s = "TestObjPlain";
}

public static void TestObjRef(ref string s)
{
    s = "TestObjRef";
}

输出:

测试平原：0 测试参考：5 TestObjPlain：test TestObjRef：TestObjRef

如何将对象传递给方法?

你在那个for object方法中做了新的吗?如果是，你必须使用ref in method。

下面的链接给你更好的想法。

http://dotnetstep.blogspot.com/2008/09/passing-reference-type-byval-or-byref.html

很多好的答案被添加了进来。我还是想做点贡献，可能会更清楚一点。

When you pass an instance as an argument to the method it passes the copy of the instance. Now, if the instance you pass is a value type(resides in the stack) you pass the copy of that value, so if you modify it, it won't be reflected in the caller. If the instance is a reference type you pass the copy of the reference(again resides in the stack) to the object. So you got two references to the same object. Both of them can modify the object. But if within the method body, you instantiate new object your copy of the reference will no longer refer to the original object, it will refer to the new object you just created. So you will end up having 2 references and 2 objects.

Objects aren't passed at all. By default, the argument is evaluated and its value is passed, by value, as the initial value of the parameter of the method you're calling. Now the important point is that the value is a reference for reference types - a way of getting to an object (or null). Changes to that object will be visible from the caller. However, changing the value of the parameter to refer to a different object will not be visible when you're using pass by value, which is the default for all types.

如果要使用引用传递，则必须使用out或ref，无论参数类型是值类型还是引用类型。在这种情况下，变量本身实际上是通过引用传递的，因此形参使用与实参相同的存储位置——调用者可以看到对形参本身的更改。

So:

public void Foo(Image image)
{
    // This change won't be seen by the caller: it's changing the value
    // of the parameter.
    image = Image.FromStream(...);
}

public void Foo(ref Image image)
{
    // This change *will* be seen by the caller: it's changing the value
    // of the parameter, but we're using pass by reference
    image = Image.FromStream(...);
}

public void Foo(Image image)
{
    // This change *will* be seen by the caller: it's changing the data
    // within the object that the parameter value refers to.
    image.RotateFlip(...);
}

我有一篇文章对此进行了更详细的介绍。基本上，“通过引用传递”并不是你所想的那样。

还有一个代码示例可以展示这一点:

void Main()
{


    int k = 0;
    TestPlain(k);
    Console.WriteLine("TestPlain:" + k);

    TestRef(ref k);
    Console.WriteLine("TestRef:" + k);

    string t = "test";

    TestObjPlain(t);
    Console.WriteLine("TestObjPlain:" +t);

    TestObjRef(ref t);
    Console.WriteLine("TestObjRef:" + t);
}

public static void TestPlain(int i)
{
    i = 5;
}

public static void TestRef(ref int i)
{
    i = 5;
}

public static void TestObjPlain(string s)
{
    s = "TestObjPlain";
}

public static void TestObjRef(ref string s)
{
    s = "TestObjRef";
}

输出:

测试平原：0 测试参考：5 TestObjPlain：test TestObjRef：TestObjRef

在c#的最新版本，即编写本文时的c# 9中，对象默认通过ref传递。因此，对调用函数中的对象所做的任何更改都将持久化在被调用函数中的对象中。