GC.Collect and WeakReferece is not to force, have other measure?

I try to solve such a problem: When the delegate is called by user, the response object of delegate
is dead (or out scope). This problem may throw an exception. 
WeakReference and GC.Collect() ?  Oh,GC  is clumsy, WeakReference.IsAlive is not realtime.
my code:

 public class Apple
    {
        public Apple() { MessageDispatch.Instance.BindingMessage(0, OnMessage); }
        public void OnMessage(object sender, EventArgs e) { Console.WriteLine("Apple,thanks."); }
    }
    public class MessageDispatch
    {
        public static readonly MessageDispatch Instance = new MessageDispatch();
        Dictionary<int, List<Pack>> _dic = new Dictionary<int, List<Pack>>();

        class Pack
        {
            public WeakReference WObject;
            public MethodInfo WEvent;
        }

        public void BindingMessage(int msgId, EventHandler e)
        {
            if (!_dic.ContainsKey(msgId))
                _dic[msgId] = new List<Pack>();

            Pack pack = new Pack();
            pack.WObject = new WeakReference(e.Target);
            pack.WEvent = e.Method;
            _dic[msgId].Add(pack);
        }

        public void PostMessage(int msgId, Object sender, EventArgs data)
        {
            if (!_dic.ContainsKey(msgId))
                return;

            //GC.Collect(); //so weight。
            foreach (Pack p in _dic[msgId]) {
                if (p.WObject.Target != null)
                    p.WEvent.Invoke(p.WObject.Target, new object[]{sender, data});
            }
        }
    }

Test：
private void Test_One()
        {
            Apple a1 = new Apple();
            CreateTempVal();
            MessageDispatch.Instance.PostMessage(0, null, EventArgs.Empty);
        }
        private void CreateTempVal()
        {
            Apple a2 = new Apple();
        }

print:

Apple,thanks.

Apple,thanks.

Used GC.Collect(), print:

Apple,thanks.

Test_One(): a1  is valid, and a2 is invalid.  if not using GC.Collect(), a1 and a2  are valid ( in my code).

The MessageDispatch is like windows message principle: Register Message (BindingMessage(msgId, ))
and post message(PostMessage(msgId, )), and then we can reponse message anywhere.

I used GC and WeakReference to solve:   outed scope object will not be called. ( void Test_One())

If this:

 void OnMouseMove(object sender, EventArgs e)
        {
            MessageDispatch.Instance.PostMessage(0, sender,e);
        }

GC will crazy.  What should i do ?

Thanks.