Example implementation of weak events using .NET's WeakEventManager

Question

Is there an example implementation of weak events using .NET's WeakEventManager?

I'm trying to implement it by following the "Notes to Inheritors" in the documentation, but it is vague. For example, I can't figure out how to call ProtectedAddListener from my static AddListener function in my custom manager.

Answer 1

I figured it out on my own following the guidelines in the "Notes for Inheritors" section of the WeakEventManager documentation. Here's a basic implementation of WeakEventManager. The class sourcing the event is named PropertyValue and the event is named Changed.

public class PropertyValueChangedEventManager : WeakEventManager
{
    public static PropertyValueChangedEventManager CurrentManager
    {
        get
        {
            var manager_type = typeof(PropertyValueChangedEventManager);
            var manager = WeakEventManager.GetCurrentManager(manager_type) as PropertyValueChangedEventManager;

            if (manager == null)
            {
                manager = new PropertyValueChangedEventManager();
                WeakEventManager.SetCurrentManager(manager_type, manager);
            }

            return manager;
        }
    }

    public static void AddListener(PropertyValue source, IWeakEventListener listener)
    {
        CurrentManager.ProtectedAddListener(source, listener);
        return;
    }

    public static void RemoveListener(PropertyValue source, IWeakEventListener listener)
    {
        CurrentManager.ProtectedRemoveListener(source, listener);
        return;
    }

    protected override void StartListening(object source)
    {
        ((PropertyValue)source).Changed += mHandler;
        return;
    }

    protected override void StopListening(object source)
    {
        ((PropertyValue)source).Changed -= mHandler;
        return;
    }

    private EventHandler mHandler = (s, e) =>
    {
        CurrentManager.DeliverEvent(s, e);
        return;
    };
}