How can I implement event acessors with DynamicObject in C #

Question

I am trying to implement a common Wrapper-Class class system for Qt using C # DynamicObject. However, I want to write the following code:

dynamic obj = new SomeWrapperClass(....); // This extends DynamicObject
obj.OnMyEvent += (Action)(() => Console.WriteLine("DO something!"));

The above code is valid in accordance with VS2010 (explicit cast to action is required), but how exactly will I "catch" this operator using DynamicObject methods?

I tried to implement TryGetMember () and it is called for an expression, but I do not know what I need to return in order to make it work.

Any clues?

Answer 1

The reflector is your friend on this. The code generated for your second line looks something like this:

if(Binder.IsEvent("OnMyEvent", typeof(SomeWrapperClass)))
{
    Binder.InvokeMember("add_OnMyEvent", obj, myAction);
}
else
{
    var e = Binder.GetMember("OnMyEvent", obj);
    var ae = Binder.BinaryOperation(ExpressionType.AddAssign, e, myAction);
    Binder.SetMember("OnMyEvent", obj, ae);
}

OnMyEvent ( DynamicObject), -, AddAssign, - . , , ...

, , OnMyEvent OnMyOtherEvent:

public class SomeWrapperClass : DynamicObject
{
    public event Action OnMyOtherEvent;

    public override bool TryGetMember(GetMemberBinder binder, out object result)
    {
        if (binder.Name == "OnMyEvent")
        {
            result = OnMyOtherEvent;
            return true;
        }
        return base.TryGetMember(binder, out result);
    }

    public override bool TrySetMember(SetMemberBinder binder, object value)
    {
        if (binder.Name == "OnMyEvent" && value is Action)
        {
            OnMyOtherEvent = (Action)value;
            return true;
        }
        return TrySetMember(binder, value);
    }

    public void Test()
    {
        if (OnMyOtherEvent != null)
            OnMyOtherEvent();
    }

    private static void TestEventHandling()
    {
        dynamic obj = new SomeWrapperClass(); // This extends DynamicObject
        obj.OnMyEvent += (Action)(() => Console.WriteLine("DO something!"));
        obj.Test();
    }
}

Answer 2

Action :

dynamic o = new SomeWrapperClass();
o.OnMyEvent += (Action)(() => Console.WriteLine("DO something!"));
var a = typeof(SomeWrapperClass).GetField("OnMyEvent", BindingFlags.Instance | BindingFlags.NonPublic);
(a.GetValue(o) as Action).Invoke();

: -!

Answer 3

, . , 'add' 'remove' , + = - = .

obj.OnMyEvent += (Action)(() => Console.WriteLine("DO something!"));

, ( ).

:

private Action actiondelegate = (Action)(() => {});

public override bool TryGetMember(GetMemberBinder binder, out object result)
{
    if (binder.Name == "OnMyEvent")
    {
        result = actiondelegate;
        return true;
    }
}

Please note that you need an empty action in the action deletion - this is because if it is zero, TryGetMemberthey TrySetMemberwill work fine.