Dictionary of Action Delegates

Question

I have object XML serialized messages coming into a class called MessageRouter. The XML contains the Type name it it was serialized from, a

Answer 1

You cannot do this as described, for quite obvious reasons - even if somehow allowed, the last line of code in your example (the one which retrieves a delegate and then calls it) would be non-typesafe, as you're calling an Action<T> - which expects T as an argument - and yet passing it deserializedObject, which is of type object. It wouldn't work in plain code without a cast, why would you expect to be able to circumvent the type check for your case?

In the simplest case, you can do something like this:

Dictionary<Type, Delegate> registeredDelegates;
...
registeredDelegates[xmlSerializedType].DynamicInvoke(deserializedObject);

Of course this will allow someone to add a delegate which takes more or less than one argument to the dictionary, and you'll only find out at DynamicInvoke call, at run-time. But there isn't really any way to define a type which says "any delegate, but with 1 argument only". A better option might be this:

Dictionary<Type, Action<object>> registeredDelegates

and then registering types like this:

myMessageRouter.RegisterDelegateForType<MySerializableType>(
   o => myActionHandler((MySerializableType)o)
);

The above snippet uses C# 3.0 lambdas, but you can do the same - if slightly more verbose - with C# 2.0 anonymous delegates. Now you don't need to use DynamicInvoke - the lambda itself will do the proper cast.

Finally, you can encapsulate the lambda creation into RegisterDelegateForType itself by making it generic. For example:

private Dictionary<Type, Action<object>> registeredDelegates;

void RegisterDelegateForType<T>(Action<T> d)
{
    registeredDelegates.Add(typeof(T), o => d((T)o));
}

And now the callers can just do:

RegisterDelegateForType<MySerializableType>(myHandler)

So it's completely typesafe for your clients. Of course, you're still responsible for doing it right (i.e. passing an object of the correct type to the delegate you retrieve from the dictionary).

Answer 2

I am not sure that this completely answers your question, but here is a class I wrote that will accomplish what you want. I couldn't tell if you want your Action delegate to take a typed object or not, but in your pseudo code, you pass it an "object" to deserialize so I wrote my class accordingly and it therefore does not use generics:

public delegate void Action(object o);

public class DelegateDictionary {
    private IDictionary _dictionary = new Hashtable();

    public void Register<T>(Action action) {
        _dictionary[typeof(T)] = action;
    }

    public Action Get<T>() {
        return (Action)_dictionary[typeof(T)];
    }

    public static void MyFunc(object o) {
        Console.WriteLine(o.ToString());
    }

    public static void Run() {
        var dictionary = new DelegateDictionary();
        dictionary.Register<string>(MyFunc);
        // Can be converted to an indexer so that you can use []'s
        var stringDelegate = dictionary.Get<string>();
        stringDelegate("Hello World");
    }
}

I believe this will accomplish what you want.