How to reflection one DLL and register it's action<string> event

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dll name is "RefTest.dll",code as below:

C#

using System;

namespace RefTest
{
    public class Test
    {
        public event Action<string> OnMessage;

        public void WriteString()
        {
            Console.WriteLine("Write String");
            OnMessage?.Invoke("ActionMessage");
        }
    }
}

Main Program as below:

C#

using System;
using System.Diagnostics;
using System.Reflection;

namespace ConsoleAppFixed
{
    class Program
    {
        static void Main(string[] args)
        {
            Assembly assembly = Assembly.LoadFrom("RefTest.dll");      
            Type typeClass = assembly.GetType("RefTest.Test");            
            object obj = Activator.CreateInstance(typeClass);                  
            MethodInfo method = typeClass.GetMethod("WriteString"); 
            method.Invoke(obj, null);                                                     


            var t = typeof(Action<string>);
            Delegate mDelegate = Delegate.CreateDelegate(t, obj, "OnMessage");

            //I don't know how to register "OnMessage" event

            Console.ReadKey();
        }

        public static void Recieve()
        {
        }
    }
}

I don't know how to regist "OnMessage",any help will be appreciated,thank you!

What I have tried:

C#

var t = typeof(Action<string>);
 Delegate mDelegate = Delegate.CreateDelegate(t, obj, "OnMessage");

 //I don't know how to register "OnMessage"

Posted 7-Sep-20 21:06pm

TabZhang

Updated 8-Sep-20 16:09pm

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2 solutions

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Richard Deeming · Accepted Answer · 2020-09-07T23:19:00

The MS documentation already covers this:
How to: Hook Up a Delegate Using Reflection | Microsoft Docs[^]

C#

Assembly assembly = Assembly.LoadFrom("RefTest.dll");      
Type typeClass = assembly.GetType("RefTest.Test");            
object obj = Activator.CreateInstance(typeClass);                  

EventInfo messageEvent = typeClass.GetEvent("OnMessage");
MethodInfo receiveMethod = typeof(Program).GetMethod("Receive", BindingFlags.Public | BindingFlags.Static);
Delegate handler = Delegate.CreateDelegate(messageEvent.EventHandlerType, null, receiveMethod);
messageEvent.GetAddMethod().Invoke(obj, new[] { handler });

MethodInfo writeStringMethod = typeClass.GetMethod("WriteString"); 
writeStringMethod.Invoke(obj, null);

NB: You'll need to update your Receive method to match the expected signature of the event - eg:

C#

public static void Receive(string message) ...

You should also follow the naming[^] and design[^] guidelines for events as far as possible:

C#

public class Test
{
    public event EventHandler<string> Message;

    public void WriteString()
    {
        Console.WriteLine("Write String");
        Message?.Invoke(this, "ActionMessage");
    }
}

C#

public static void Receive(object sender, string message) { ... }

In an ideal world, the second argument to the event would be a class derived from System.EventArgs. But unless you can find a built-in one that suits your requirements, it could be tricky to create a custom class which is shared between the RefTest assembly and the calling assembly.

TabZhang · Accepted Answer · 2020-09-08T16:09:00

Thanks Richard! I find use interface is a better way.

dll and MainProgram both can reference the Interface.

Interface Code:

C#

using System;

namespace MyInterface
{
    public interface ITestAction
    {
        string FailReason { get; set; }

        event Action<string> OnTestStart;

        void RunTest();

    }
}

DLL Code:

C#

using MyInterface;
using System;

namespace RefTest
{
    public class Test : ITestAction
    {
        public string FailReason { get; set; }

        public event Action<string> OnTestStart;

        public void RunTest()
        {
            try
            {
                Console.WriteLine("Write String");
                OnTestStart?.Invoke("ActionMessage");
            }
            catch (Exception ex)
            {
                FailReason = ex.Message;
            }
        }
    }
}

Main Program Code:

C#

using System;
using System.Reflection;
using MyInterface;

namespace ConsoleAppFixed
{
    class Program
    {
        static void Main(string[] args)
        {
            Assembly assembly = Assembly.LoadFrom("RefTest.dll");
            Type typeClass = assembly.GetType("RefTest.Test");
            ITestAction obj = (ITestAction)Activator.CreateInstance(typeClass);

            if (obj != null)
            {
                obj.OnTestStart += ITestAction_OnTestStart;
                obj.RunTest();
            }

            Console.ReadKey();
        }

        private static void ITestAction_OnTestStart(string obj)
        {
            Console.WriteLine(obj);
        }


    }
}

How to reflection one DLL and register it's action<string> event

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