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我想将代码注入外部方法，而不编辑源代码。我已经可以替换当前方法来引用我自己的方法，因为动态替换 C# 方法的内容？.

我仍然需要能够在运行时修改外部方法体，这意味着能够在方法调用之前和方法调用之后注入代码。

我不能 手动调用我想修改的这个方法。是一个自己运行的服务。

我努力了：

  1. Reflection.Emit -> 但这会创建一个未被引用的新方法。
  2. Marshall -> Marshal.GetFunctionPointerForDelegate，然后将方法替换为之后调用编组函数 -> 不起作用，因为替换是指针并且 marhal 更改了指针。

情况：

    class Program
    {
        static void Main(string[] args)
        {
            var oldMethod = typeof(InstanceClassA).GetMethod("OldMethod", BindingFlags.Instance | BindingFlags.Public);
            var beforeMethod = typeof(InstanceClassA).GetMethod("BeforeMethod", BindingFlags.Instance | BindingFlags.Public);

            oldMethod.Before(() => Console.WriteLine("Called Before"));
            oldMethod.Before(() => beforeMethod);

            //This is *TESTING* only as I can't manually call the method i want to inject.

            var instance = new InstanceClassA();
            //Should now call the beforeMethod and the called before
            instance.OldMethod("With Before");
            //Should call the after method

            Console.ReadLine();
        }
    }

    public static class MethodInfoUtils
    {
        //Will *NOT* allow return values as this should return oldMethod return value
        //Will allow Actions and another MethodInfo
        public static void Before(this MethodInfo method)
        {
            // Code to inject code before calling the external method
        }

        //Will *NOT* allow return values as this should return oldMethod return value
        //Will allow Actions and another MethodInfo
        public static void After(this MethodInfo method)
        {
            // Code to inject code after calling the external method
        }
    }

    public class InstanceClassA
    {
        public bool OldMethod(string message)
        {
            Console.WriteLine(message);
            return true;
        }

        //message param is equal to the oldMethod param as it is called before the oldMethod is called
        public void BeforeMethod(string message)
        {
            Console.WriteLine("test");
        }
    }
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