Ytukyg

I have used reflection in my project to add events to ObservableCollections - specifically, CollectionChanged. I am able to add the event well enough and there is no problem there. The problem is that the code to add the event is run more than once and so I end up with multiple identical events added in some cases. What I don't know how to do is either check to see if there is already an event assigned, or to remove before I add one (to ensure there is only one event added).

The code is here:

foreach (PropertyInfo propertyInfo in props)

{

    nType = this.GetPropertyInfoTypeObs(propertyInfo.PropertyType);



    if (nType == Static_Enums.TypeEnums.TYPE_OBSERVABLE_COLLECTION)

    {

        var genargs = propertyInfo.PropertyType.GetGenericArguments();



        var o = propertyInfo.GetValue(this, null);



        EventInfo evi = o.GetType().GetEvent("CollectionChanged", BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance);

        var eventHandler = new Action<object, NotifyCollectionChangedEventArgs>(

                    (s, a) =>

                    {

                        // Event code here

                        this.MakePropertyDirty(propertyInfo.Name);

                    });



        var del = Delegate.CreateDelegate(evi.EventHandlerType, eventHandler.Target, eventHandler.Method);



        evi.AddEventHandler(o, del);

    }

}

As stated, this part works fine. But how to handle the issue of the event being added more than once?

I first tried simply having evi.RemoveEventHandler(o, del) on the line above. This doesn't work for me - as in, if I watch what happens when that line is executed, the event handler seems to remain untouched. Perhaps I'm doing it incorrectly?

I'd also be happy with a way to check if the event handler already has one assigned, and then skip over adding it again. But how to do that I've no idea.

Edit

I have tried creating the delegate as a class property in order that it can persist. But even still, as I trace over the lines, I can see that the handler is not removed when I call the evi.RemoveEventHandler with this property delegate.

I then went a little further and tried doing this:

EventInfo ef = o.GetType().GetEvent("CollectionChanged");

MethodInfo rem = ef.GetRemoveMethod();

ParameterInfo piList = rem.GetParameters();



object oList = new object[1];

oList[0] = storedProc;



rem.Invoke(o, oList);

Unfortunately it also doesn't seem to do the trick.

Furthermore, I read that in order to remove a handler, it has to be the exact same handler in the remove method. Now, in this method here, the derived class has more than one ObservableCollection. So I tried limiting the creation of the new delegate (and assigning it to the class property) to only in the case of a particularly named ObservableCollection (one I knew would appear). I traced it over again, one line at a time, and the event handler was not removed.

Even if this did work, however, I'd then have to store a delegate for each ObservableCollection for which I did this. My god, can't I just tell it to clear the event?