Handle Generic methods in a dictionary according to type

问题

I have a generic method

public delegate void Handler<T>(T val);

I enable users to register to events and provide this delegate. I need to save the list of delegate according to their types.

I tried saving in a dictionary of Type and object. when adding the method I cast it to a

List<Handler<T>>

according to the T. but then when an event occurred I do not have the T so cannot cast to the relevant list of generic handlers (I do have the Type but not the T)

I solved this by saving methodInfo list for each type

  private Dictionary<Type, List<MethodInfo>>  handlers = new Dictionary<Type, List<MethodInfo>>();

    public delegate void Handler<T>(T val);


    public void Register<T>( Handler<T> handler )
    {
        List<MethodInfo> lst;
        if (!handlers.TryGetValue(typeof(T), out lst))
        {
            lst = new List<MethodInfo>();
            handlers.Add(typeof(T), lst);
        }
       lst.Add(handler.Method);

    }

    public void RaiseEvent( string value)
    {
       foreach (KeyValuePair<Type, List<MethodInfo>> pair in handlers)
            {
                object typedValue;

                if (pair.Key.IsEnum)
                {
                    typedValue = Enum.Parse(pair.Key, value);
                }
                else
                {
                    typedValue = Convert.ChangeType(value, pair.Key);
                }

                foreach (MethodInfo  methodInfo  in pair.Value )
                {
                    methodInfo.Invoke(null, new[] { typedValue });
                }
            }
        }
    }

but the problem is that this approach will work only if the method is static , otherwise it will require the type of class.

is there any solution for this problem???

enable generic events... thanks!

回答1:

Maybe this will help:

public delegate void Handler<in T>(T val);

private List<Delegate> m_list = new List<Delegate>();

public void AddListener<T>(Handler<T> handler) {
  m_list.Add(handler);
}

public void Call(object eventArg) {
  foreach (var handler in m_list) {
    handler.DynamicInvoke(eventArg);
  }
}

Then, if you have a handler like this:

private void MyHandler(int val) {
  // Do something
}

You can add it to the list like this:

AddListener<int>(MyHandler);

(This assumes I correctly understood what you're trying to do. I'm not sure though.)

回答2:

You could also make a handler repository using a non-generic delegate, something like:

public delegate void Handler(object val);
public delegate void Handler<T>(T val);

public class HandlerRepository
{
  private Dictionary<Type, Handler>  handlers = new Dictionary<Type, Handler>();

  public void RegisterHandler<T>(Handler<T> handler)
  {
     //error checking omitted
     //create a non-generic handler that calls the generic handler 
     //with the correct type.
     handlers.Add(typeof(T), (value)=>handler((T)value));
  }

  public void ExecuteHandler<T>(T value)
  {
     //error checking ommited
     handlers[typeof(T)](value);
  }
}

and use it like this:

Handler<int> handleInt = value => Console.WriteLine("Int32 is {0}", value);
Handler<string> handleString = value => Console.WriteLine("String is {0}", value);
HandlerRepository repo = new HandlerRepository();
repo.RegisterHandler(handleInt);
repo.RegisterHandler(handleString);

//this call boxes the argument to an object   
repo.ExecuteHandler(5);  // "Int32 is 5"
repo.ExecuteHandler("Hello, world"); "String is Hello, world"

来源：https://stackoverflow.com/questions/14496989/handle-generic-methods-in-a-dictionary-according-to-type

标签

generics

delegates

methodinfo

method-invocation