Question

I have this method:

public override void respond(params string[] resargs)
{
    foreach (command cmd in pndgcmds)
    {
        cmd(this);
    }

    if (objs[resargs[0]].status)
        objs[resargs[0]].request(resargs);
    else
    {
        pndgcmds.Add(
            (myclass master) =>
            {
                if (master.objs[resargs[0]].status != true) return;
                master.objs[resargs[0]].request(resargs);
                //code to remove the delegate
            });
    }
}

which checks if an object is able to respond, makes it respond if it does, otherwise stores the command in a dictionary so that the status is checked and called the next time a respond is called.

I have two questions.

1. How do I write code to remove the delegate? I have no idea how to do that.

2. As you can see, much of the inner workings of the delegate relies on method parameters. How will the delegate behave?

Thanks in advance!

Answer 1

Anonymous methods are a pain to remove, as the instance of the captire-context is only available when creating it, an is required. Fortunately, there’s a trick:

SomeDelegateType handler = null;
handler = (myclass master) =>
            {
                if (master.objs[resargs[0]].status != true) return;
                master.objs[resargs[0]].request(resargs);
                pndgcmds.Remove(handler);
            };
pndgcmds.Add(handler);

This is now a self-unsubscribing handler, that will unsubscribe itself when invoked. Note that to do this we need to store the delegate instance (handler), but we then create a closure over that variable. The initial =null is a requirement of definite assignment.

You should note that the resargs variable is also captured, and this could lead to confusion if the value at index-zero changes after subscription but before it is invoked. If you want to use the value “now”, then close over that instead:

SomeDelegateType handler = null;
string val = resargs[0];
handler = (myclass master) =>
            {
                if (master.objs[val].status != true) return;
                master.objs[val].request(resargs);
                pndgcmds.Remove(handler);
            };
pndgcmds.Add(handler);