在不使用静态类的情况下调用类的扩展方法，而是通过使用反射使用类iteslf

Question

I want invoke Method2 which is an extension method of a MyClass using MyClass type. I am wondering if this is possible or not.

using System;
using System.Linq;
using System.Reflection;

namespace ConsoleApplication9
{
    public static class MyClassStatic
    {
        public static void Method2(this ConsoleApp2.MyClass obj)
        {
            Console.WriteLine("You have called ex Method 2");
        }
    }

    public interface IClass
    {
        void Method1();
    }

    public class MyClass : ConsoleApp2.IClass
    {
        public void Method1()
        {
            Console.WriteLine("You have called Method 1");
        }
    }

    class Program
    {


        public static void CallWhereMethod()
        {


            var whereMethods = typeof(MyClass)
                .GetMethods(BindingFlags.Static | BindingFlags.Public)
                .Where(mi => mi.Name == "Method2");


            Console.WriteLine(whereMethods.Count());
            // returns zero

        }

        static void Main(string[] args)
        {
            CallWhereMethod();
            Console.ReadKey();

        }

    }
}

Answer 1

Actually, there is a way for this, but it's hard a bit. If you don't forget to place a this keyword to your extension method parameter, C# compiler will emmit ExtensionAttribute to this method and this class. Knowing this, you are able to find this extension method and execute it:

var myClassType = typeof(MyClass);
var myClass = new MyClass();

var assemblyTypes = Assembly.GetExecutingAssembly().GetTypes();
foreach (var type in assemblyTypes.Where(t => t.GetCustomAttribute<ExtensionAttribute>() != null)
{
    var typeMethods = type.GetMethods(BindingFlags.Static | BindingFlags.Public | BindingFlags.NonPublic);
    foreach (var method in typeMethods.Where(m => m.IsDefined(typeof(ExtensionAttribute), inherit: false))
    {
        if (method.GetParameters()[0].ParameterType == myClassType)
        {
            // here you go
            method.Invoke(null, new object[]{ myClass });
        }
    }
}

If you unsure in which assembly to search for extension method, you may try to search all :

var allLoadedTypes = AppDomain.CurrentDomain.GetAssemblies().SelectMany(a => a.GetTypes());

Please note: reflection is slow . Really slow. Even you filter all of your types with .Where(type => type.IsSealed) or any other filter, it is still dead slow . If you have any other way to invoke the code in your extension method, you probably should use that way.

Answer 2

Sure its possible, the only caveat is .Net Reflection doesn't understand the Extension Method syntactic-sugar of this .

Remembering, that an extension method is a C# construct to save you a couple of printable-characters when calling a static class static method when given the first parameter (labelled with the this keyword)

So in-Short, you'll have to target the static class and pass in the MyClass instance as the first parameter

var myClass = new MyClass();

var whereMethods = typeof(MyClassStatic)
                  .GetMethods(BindingFlags.Static | BindingFlags.Public)
                  .FirstOrDefault(mi => mi.Name == "Method2");

whereMethods.Invoke(null, new object[]{ myClass } );

Output

You have called ex Method 2

Full Demo Here

Update

I dont want to use typeof(MyClassStatic).. I want to use typeof(MyClass)

Method2 is not a member of MyClass , and you cant force it to be as such in any way that i can think of.