事件可能會(huì)引起一個(gè)內(nèi)存泄露問(wèn)題，而該模型就是為了解決該問(wèn)題。

為什么會(huì)出現(xiàn)memory Leak

事件的使用語(yǔ)法如：source.Event+=Listener.Func，這樣Source即建立了一個(gè)Listener的強(qiáng)引用，從而Listener的生命周期將受到Source的影響，生命周期延長(zhǎng)，從而產(chǎn)生內(nèi)存泄露。

如何完成弱事件模型

1. 從WeakEventManager派生出一個(gè)Manager。
2. 在Listerner對(duì)象上實(shí)現(xiàn)IWeakEventListener接口。
3. 當(dāng)對(duì)Source添加Listener時(shí)，不要使用事件的Add或Remove操作，應(yīng)該使用Manager中的AddListener及RemoveListener。

自定義WeakEventManager

• 重寫(xiě)StartListening及StopListening
• 提供兩個(gè)方法來(lái)操作Listeners List，常用命名為Addlistener及RemoveListener
• 實(shí)現(xiàn)一個(gè)CurrentManager屬性

代碼示例

    class Source
    {
        public void Time()
        {
            var timeHandler = TimeChanged;
            if (null != timeHandler)
                timeHandler(this, new TimeEventArgs { TimeNow = DateTime.Now });
        }

        public event Action<object, TimeEventArgs> TimeChanged;
    }

    class TimeChangeEventManager : WeakEventManager
    {
        private static TimeChangeEventManager CurrentManager
        {
            get
            {
                var manager = (TimeChangeEventManager)GetCurrentManager(typeof(TimeChangeEventManager));

                if (manager == null)
                {
                    manager = new TimeChangeEventManager();
                    SetCurrentManager(typeof(TimeChangeEventManager), manager);
                }

                return manager;
            }
        }

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

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

        protected override void StartListening(object source)
        {
            ((Source)source).TimeChanged += DeliverEvent;
        }

        protected override void StopListening(object source)
        {
            ((Source)source).TimeChanged -= DeliverEvent;
        }
    }

    class ListenerTwo : IWeakEventListener
    {
        private static int S_ListenCount = 0;

        private int _currentIndex = 0;

        public ListenerTwo()
        {
            _currentIndex = S_ListenCount++;
        }

        public void Show(object sender, TimeEventArgs e)
        {
            Console.WriteLine("Index: {0} Time: {1}", _currentIndex, e.TimeNow);
        }

        public bool ReceiveWeakEvent(Type managerType, object sender, EventArgs e)
        {
            if (managerType == typeof (TimeChangeEventManager))
                Show(sender, (TimeEventArgs) e);
            else
            {
                return false;
            }
            return true;
        }
    }

    class TimeEventArgs : EventArgs
    {
        public DateTime TimeNow { get; set; }
    }
            static void Main(string[] args)
        {
            Source ss = new Source();
            AddListener(ss);
            ss.Time();
            Console.Read();
        }

        private static void AddListener(Source ss)
        {
            var lis1 = new ListenerTwo();
            var lis2 = new ListenerTwo();
            //可以釋放
            TimeChangeEventManager.AddListener(ss,lis1);
            TimeChangeEventManager.AddListener(ss,lis2);
            //不會(huì)釋放
            ss.TimeChanged += lis1.Show;
            ss.TimeChanged += lis2.Show;
            lis1 = null;
            lis2 = null;
            GC.Collect();
        }

.Net 4.5的處理方式

4.5提供了WeakEventManager的一個(gè)泛型版本，即WeakEventManager<TEventSource,TEventArgs>。使用泛型版本則不需要自定義一個(gè)新的EventManager類(lèi)。
用法相當(dāng)?shù)暮?jiǎn)單，如下代碼所示：
WeakEventManager<Source, TimeEventArgs>.AddHandler(ss, "TimeChanged", lis1.Show);

引用

http://www.codeproject.com/Articles/738109/The-NET-weak-event-pattern-in-Csharp
https://msdn.microsoft.com/en-us/library/aa970850(v=vs.100).aspx
https://msdn.microsoft.com/en-us/library/system.windows.iweakeventlistener.receiveweakevent(v=vs.100).aspx
https://msdn.microsoft.com/en-us/library/system.windows.weakeventmanager(v=vs.100).aspx