Referencing asynchronous tasks in a c# dictionary

Question

I've come across the problem regarding asynchronous tasks in a dictionary in a couple programs now, and I can't wrap my head around how to solve it.

I have an asynchronous task that looks like this:

MessageEventArgs.Channel.SendMessage("somestring");

MessageEventArgs is a class from a 3rd party library that I declare statically at the start of my program:

public static MessageEventArgs meargs;

The program listens for events in an IRC channel and does actions based on text commands. Rather than have a giant switch statement for each command, I wanted to make a dictionary that matched the string to the method. Not all are simply sending messages, so I can't just store the string to send. It looks like this:

public static Dictionary<string, Task> myDict= new Dictionary<string, Task>()
{
    {"!example", MessageEventArgs.Channel.SendMessage("HelloWorld") }
}

In Main(), I call:

MessageReceived += async (s,e) => 
{
     meargs = e;
     await myDict[e.Message.Text];
}

What I've come to realize is that when the dictionary is instantiated, it tries to call SendMessage, as it is an async task. MessageEventArgs isn't instantiated until after, so it throws an exception. Is there a way to go about storing a reference to these functions in a dictionary? I found solutions using delegates, but they didn't seem to work with void methods, and async methods (to my knowledge) can only return void or Task.

Thanks in advance!

Answer 1

Instead of creating the tasks immediately, store factories:

public static Dictionary<string, Func<Task>> myDict= new Dictionary<string, Func<Task>>()
{
    {"!example", () => MessageEventArgs.Channel.SendMessage("HelloWorld") }
}

await myDict[e.Message.Text]();

Answer 2

If I were writing this, I would create an IrcCommand class with a virtual ExecuteCommand function. Then create a subclass for every distinct command I wanted to be able to run. Each subclass would override the ExecuteCommand function with the logic needed to invoke the command. ExecuteCommand could take an argument of type Channel corresponding the the channel to invoke the command.

At startup I would create a Dictionary<string, IrcCommand> that was populated with a Key of the command text, and a Value of a new instance of the subclass implementing that command.

When a command comes in I would pull the IrcCommand instance from the dictionary with the matching key and call the ExecuteCommand function on it, passing in the Channel the command was received from.

---

It could happen something like this. I don't actually have visual studio open to verify my syntax, so I may have a few errors in here.

An implementation of some commands:

public class ExampleCommand : IrcCommand
{
    public override void ExecuteCommand(Channel channel)
    {
        channel.SendMessage("Hello World");
    }
}

public class DisconnectCommand : IrcCommand
{
    public override void ExecuteCommand(Channel channel)
    {
        channel.Disconnect();
    }
}

---

Registering commands at application start:

private void RegisterCommands()
{
    _commands.add("!example", new ExampleCommand());
    _commands.add("!disconnect", new DisconnectCommand());
}

---

Executing the command when received:

_commands(commandText).ExecuteCommand(e.channel);