观察者模式

    /// <summary>
    /// 事件提供者
    /// </summary>
    public class EventProvider
    {
        //弱引用事件处理器
        private WeakReference<EventHandler<EventArgs>> _event = new WeakReference<EventHandler<EventArgs>>(null);

        public event EventHandler<EventArgs> Event
        {
            add
            {
                _event.Target += value;
            }
            remove
            {
                _event.Target -= value;
            }
        }
        public void Notify(object sender, EventArgs e)
        {
            if (_event != null && _event.Target != null)
                _event.Target(sender, e);
        }
    }

/// <summary>
    /// 泛型WeakReference
    /// </summary>
    /// <typeparam name="T"></typeparam>
    public class WeakReference<T> : WeakReference where T : class
    {
        public WeakReference() : base(null) { }
        public WeakReference(T target) : base(target) { }
        public WeakReference(T target, bool trackResurrection) : base(target, trackResurrection) { }
        public WeakReference(SerializationInfo info, StreamingContext context) : base(info, context) { }

        public new T Target
        {
            get
            {
                return base.Target as T;
            }
            set
            {
                base.Target = value;
            }
        }

        public static implicit operator T(WeakReference<T> o)
        {

            if (o != null && o.Target != null)
                return o.Target;
            return null;
        }

        public static implicit operator WeakReference<T>(T target)
        {
            return new WeakReference<T>(target);
        }
    }

class App
    {
        private byte[] memory = new byte[10000000];

        public void TestWeakDel(object sender, EventArgs args)
        {
            MessageBox.Show("TestWeakDel");
        }
    }

EventProvider ep = new EventProvider();
            List<EventHandler<EventArgs>> list = new List<EventHandler<EventArgs>>();

            App app = new App();
            EventHandler<EventArgs> tmp = new EventHandler<EventArgs>(app.TestWeakDel);
            ep.Event += tmp;
            ep.Notify(app, EventArgs.Empty);
            app = null;
            GC.Collect();