Weak Eventの実装？

eventsource.cs

namespace WonderfulPanda.Gist
{
  public class EventSourceSample
  {
    WeakEvent<EventArgs> _test = new WeakEvent<EventArgs>();
    public event Test
    {
      add { _test.AddHandler(value); }
      remove { _test.RemoveHandler(value); }
    }
	  
    protected virtual OnTest(EventArgs e)
    {
      _test.RaiseEvent(e);
    }
  }
}

weakevent.cs

namespace WonderfulPanda.Gist
{
  public class WeakEvent<TEventArgs> where TEventArgs: EventArgs
  {
    List<WeakReference> _handlers = new List<WeakReference>();

    public void AddHandler(EventHandler<TEventArgs> handler)
    {
      lock (_handlers)
      {
        _handlers.Add(new WeakReference(handler));
      }
    }

    public void RemoveHandler(EventHandler<TEventArgs> handler)
    {
      lock (_handlers)
      {
        _handlers.RemoveAll(w => !w.IsAlive || ((EventHandler<TEventArgs>)w.Target) == handler);
      }
    }

    public void RaiseEvent(object sender, TEventArgs e)
    {
      EventHandler<TEventArgs> []handlers;
      lock (_handlers)
      {
        handlers = _handlers.Where(w => w.IsAlive)
                            .Select(w => w.Target as EventHandler<TEventArgs>)
                            .Where(h => h != null)
                            .ToArray();
        _handlers.RemoveAll(w => !w.IsAlive);
      }
      foreach (var h in handlers)
        h(sender, e);
    }
  }
}