如何在单独的文件中实现事件处理程序并使用依赖注入附加它？

Question

I'm using Discord.Net to create a C# Discord bot. My application is using Dependency Injection and in the Program.cs file I have access to the singleton instance of DiscordSocketClient .

This instance provides many events eg

discordSocketClient.UserJoined += async socketGuildUser =>
{
    // do things here
};

This seems to be a more C# related question. I want to create separate files with one event handler per file to keep the code organized. A sample event handler could look like

public class UserJoinedHandler
{
    // Use the constructor to get access to services by using DI 

    public Task OnUserJoined(SocketGuildUser socketGuildUser)
    {
        // Do things here
        
        return Task.CompletedTask;
    }
}

---

What is the best / easiest way to attach this event listener? The first solution coming to my mind would be to register this handler as a singleton service

serviceCollection.AddSingleton<UserJoinedHandler>();

and in my Program.cs file I could then do this

discordSocketClient.UserJoined += serviceProvider.GetService<UserJoinedHandler>().OnUserJoined;

---

Are there any better solutions to register handlers? Eg using reflection or annotations like [ThisClassHandlesTheUserJoinedEvent] and let the client search for those by adding an extension method like discordSocketClient.SearchForEventHandlingAnnotations() ?

I know this sounds like overengineering but this project is a big one and I like organized code.

Answer 1

This is more of a half answer/half comment.

Be careful not to overuse dependency injection. It's a great tool to help you avoid tight coupling in your code and make testing of dependent services easier but it's not meant to help you organize your code.

In your case you don't really have a dependent service - ie a service that depends on your handlers. This means there's really nothing to inject them into. Yes, you could create a wrapper class you can inject into that collects and registers all the handlers but does it really add any value to you?

If I were you I would just have a helper class to RegisterClientHandlers and then subscribe your handlers to all the events in there. If you then down the line think you need to be able to test different combinations of handlers (say UserJoinedHandler_v2 together with UserLeftHandler_v1 ), then you could start to think about making those injectable into the helper class using a common handler-interface.