当你将System.Drawing.Image类型对象传递给一个方法时，你实际上是在传递该对象引用的副本。

如果在这个方法中你要加载一个新图像你是在使用new/ replicated reference来加载。你没有改变原来的样子。

YourMethod(System.Drawing.Image image)
{
    //now this image is a new reference
    //if you load a new image 
    image = new Image()..
    //you are not changing the original reference you are just changing the copy of original reference
}

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.

我想当你这样做的时候会更清楚。我建议下载LinqPad来测试这样的事情。

void Main()
{
    var Person = new Person(){FirstName = "Egli", LastName = "Becerra"};

    //Will update egli
    WontUpdate(Person);
    Console.WriteLine("WontUpdate");
    Console.WriteLine($"First name: {Person.FirstName}, Last name: {Person.LastName}\n");

    UpdateImplicitly(Person);
    Console.WriteLine("UpdateImplicitly");
    Console.WriteLine($"First name: {Person.FirstName}, Last name: {Person.LastName}\n");

    UpdateExplicitly(ref Person);
    Console.WriteLine("UpdateExplicitly");
    Console.WriteLine($"First name: {Person.FirstName}, Last name: {Person.LastName}\n");
}

//Class to test
public class Person{
    public string FirstName {get; set;}
    public string LastName {get; set;}

    public string printName(){
        return $"First name: {FirstName} Last name:{LastName}";
    }
}

public static void WontUpdate(Person p)
{
    //New instance does jack...
    var newP = new Person(){FirstName = p.FirstName, LastName = p.LastName};
    newP.FirstName = "Favio";
    newP.LastName = "Becerra";
}

public static void UpdateImplicitly(Person p)
{
    //Passing by reference implicitly
    p.FirstName = "Favio";
    p.LastName = "Becerra";
}

public static void UpdateExplicitly(ref Person p)
{
    //Again passing by reference explicitly (reduntant)
    p.FirstName = "Favio";
    p.LastName = "Becerra";
}

然后输出

WontUpdate

名:Egli，姓:Becerra

更新隐式

名:法维奥，姓:贝塞拉

UpdateExplicitly

名:法维奥，姓:贝塞拉

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。

在Pass By Reference中，只在函数参数和一个参数中添加“ref” 更多的事情你应该声明函数“static”，因为main是静态的(#public void main(String[] args))!

namespace preparation
{
  public  class Program
    {
      public static void swap(ref int lhs,ref int rhs)
      {
          int temp = lhs;
          lhs = rhs;
          rhs = temp;
      }
          static void Main(string[] args)
        {
            int a = 10;
            int b = 80;

  Console.WriteLine("a is before sort " + a);
            Console.WriteLine("b is before sort " + b);
            swap(ref a, ref b);
            Console.WriteLine("");
            Console.WriteLine("a is after sort " + a);
            Console.WriteLine("b is after sort " + b);  
        }
    }
}