传统事件publisher和listener是直接相连的，这样会对垃圾回收带来一些问题，例如listener已经不引用任何对象但它仍然被publisher引用

垃圾回收器就不能回收listener所占用的内存以及publisher仍然引用该listener向其触发事件。

而弱事件就解决了这个问题

WeakEventManager是publisher和listener之间的桥梁，从而取代两者之间的直接连接

一、定义WeakEventManager类

public class WeakCarInfoEventManager : WeakEventManager
    {
        public static void AddListener(object source,IWeakEventListener listener)
        {
            CurrentManager.ProtectedAddListener(source, listener);
        }
        public static void RemoveListener(object source,IWeakEventListener listener)
        {
            CurrentManager.ProtectedRemoveListener(source, listener);
        }
        public static WeakCarInfoEventManager CurrentManager
        {
            get
            {
                var manager = GetCurrentManager(typeof(WeakCarInfoEventManager))
                    as WeakCarInfoEventManager;
                if(manager == null)
                {
                    manager = new WeakCarInfoEventManager();
                    SetCurrentManager(typeof(WeakCarInfoEventManager), manager);
                }
                return manager;
            }
        }
        protected override void StartListening(object source)
        {
            (source as CarDealer).NewCarInfo += CarDealer_NewCarInfo;
        }
        void CarDealer_NewCarInfo(object sender,CarInfoEventArgs e)
        {
            DeliverEvent(sender, e);
        }
        protected override void StopListening(object source)
        {
            (source as CarDealer).NewCarInfo -= CarDealer_NewCarInfo;
        }
    }

二、定义事件监听者(listener)

public class Consumer:IWeakEventListener //主要要继承改接口
    {
        private string name;
        public Consumer(string name)
        {
            this.name = name;
        }
        public void NewCarIsHere(object sender,CarInfoEventArgs e)
        {
            Console.WriteLine("{0}:car {1} is new", name, e.Car);
        }
        bool IWeakEventListener.ReceiveWeakEvent(Type managerType,object sender,EventArgs e)
        {
            NewCarIsHere(sender, e as CarInfoEventArgs);
            return true;
        }
    }

三、事件发布者(publisher)

public class CarInfoEventArgs : EventArgs //自定义事件数据参数
    {
        public CarInfoEventArgs(string car)
        {
            this.Car = car;
        }
        public string Car { get; private set; }
    }
    public class CarDealer
    {
        public event EventHandler<CarInfoEventArgs> NewCarInfo;
        public void NewCar(string car)
        {
            Console.WriteLine("Car dealer, new car {0}", car);
            RaiseNewCarInfo(car);
        }
        protected virtual void RaiseNewCarInfo(string car)
        {
            EventHandler<CarInfoEventArgs> newCarInfo = NewCarInfo;
            if (newCarInfo != null)
            {
                newCarInfo(this, new CarInfoEventArgs(car));
            }
        }
    }

四、在启动函数中通过WeakCarInfoEventManager把publisher和listener联系起来

class Program
    {
        static void Main(string[] args)
        {
            var dealer = new CarDealer();
            var tian = new Consumer("tian");
            WeakCarInfoEventManager.AddListener(dealer, tian);

dealer.NewCar("奔驰");

var tian1 = new Consumer("tian1");
            WeakCarInfoEventManager.AddListener(dealer, tian1);

dealer.NewCar("东风");
            Console.ReadKey();
        }
    }

运行结果如下：

最后.net4.5版本已经将weakeventmanager集成进来这样使用会更加方便

static void Main(string[] args)
        {
            var dealer = new CarDealer();
            var tian = new Consumer("tian");
            //WeakCarInfoEventManager.AddListener(dealer, tian);
            WeakEventManager<CarDealer, CarInfoEventArgs>.AddHandler(dealer, "NewCarInfo", tian.NewCarIsHere);

dealer.NewCar("奔驰");

var tian1 = new Consumer("tian1");
            //WeakCarInfoEventManager.AddListener(dealer, tian1);
            WeakEventManager<CarDealer, CarInfoEventArgs>.AddHandler(dealer, "NewCarInfo", tian1.NewCarIsHere);

dealer.NewCar("东风");
            Console.ReadKey();
        }

与上面的运行结果是一样的