C#_事件委托

CarDealer类 事件发布程序

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DelegateEvent
{
    public class CarInfoEventArgs : EventArgs
    {
        public string Car { get; private set; }
        public CarInfoEventArgs(string car)
        {
            this.Car = car;
        }
    }
    /// <summary>
    /// 新车到达时触发的事件
    /// </summary>
    public class CarDealer
    {
        /*
         * 泛型委托EventHandler<T>定义了一个处理程序，返回Void,接受两个参数
         * 第一个参数必须为object，第二个参数是T类型
         * T有约束,T必须派生自基类EventArgs
         * 即public delegate void EventHandler<TEventArgs>(object sender,TEventArgs e) 
         *      where TeventArgs:EventArgs
         */
      
        public event EventHandler<CarInfoEventArgs> NewCarInfo;
        public void NewCar(string car)
        {
            Console.WriteLine("CarDealer ,new car {0}",car);
            RaiseNewCarInfo(car);
        }

        protected virtual void RaiseNewCarInfo(string car)
        {
            EventHandler<CarInfoEventArgs> newCarInfo = NewCarInfo;
            if (newCarInfo != null)
            {
                //事件一般使用带两个参数的方法，其中一个参数是对象包含事件的发送者
                //第二个参数提供了事件的相关信息，第二个参数随不同的事件类型而不同
                newCarInfo(this, new CarInfoEventArgs(car));
            }
        }
    }
}

Consumer类 事件监听器

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DelegateEvent
{
    /// <summary>
    /// 事件订阅类
    /// </summary>
    class Consumer
    {
        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);
        }
    }
}

测试类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DelegateEvent
{
    class Program
    {
        static void Main(string[] args)
        {
            var dealer = new CarDealer();
            var michael = new Consumer("A"); //订阅者A
            dealer.NewCarInfo += michael.NewCarIsHere;
            dealer.NewCar("A_Car"); //A车到达 A得到通知

            var sebastian = new Consumer("B"); //订阅者B
            dealer.NewCarInfo += sebastian.NewCarIsHere;
            dealer.NewCar("B_Car"); //B车到达 A、B都得到通知

            dealer.NewCarInfo -= michael.NewCarIsHere; //A取消订阅
            dealer.NewCar("C_Car"); //C车到达 只有B得到通知
        }
    }
}

测试结果

上述代码的不足体现在事件发布程序和事件监听器进行强连接。

添加弱事件管理器WeakCarInfoEventManager

using System.Windows;

namespace DelegateEvent
{
    /// <summary>
    /// 弱事件管理器
    /// </summary>
    public class WeakCarInfoEventManager : WeakEventManager
    {
        /// <summary>
        /// 发布程序
        /// </summary>
        /// <param name="source"></param>
        /// <param name="listener"></param>
        public static void AddListener(object source, IWeakEventListener listener)
        {
            CurrentManager.ProtectedAddListener(source, listener);
        }

        /// <summary>
        /// 断开发布程序
        /// </summary>
        /// <param name="source"></param>
        /// <param name="listener"></param>
        public static void RemoveListener(object source, IWeakEventListener listener)
        {
            CurrentManager.ProtectedRemoveListener(source, listener);
        }

        public static WeakCarInfoEventManager CurrentManager
        {
            get
            {
                WeakCarInfoEventManager manager = GetCurrentManager(typeof(WeakCarInfoEventManager)) as WeakCarInfoEventManager;
                if (manager == null)
                {
                    manager = new WeakCarInfoEventManager();
                    SetCurrentManager(typeof(WeakCarInfoEventManager), manager);
                }
                return manager;
            }
        }

        /// <summary>
        /// 订阅一个方法
        /// </summary>
        /// <param name="source"></param>
        protected override void StartListening(object source)
        {
            (source as CarDealer).NewCarInfo += CarDealer_NewCarInfo;
        }

        void CarDealer_NewCarInfo(object sender, CarInfoEventArgs e)
        {
            DeliverEvent(sender, e);
        }
        /// <summary>
        /// 取消订阅一个方法
        /// </summary>
        /// <param name="source"></param>
        protected override void StopListening(object source)
        {
            (source as CarDealer).NewCarInfo -= CarDealer_NewCarInfo;
        }
    }
}

更正事件监听器为WeakConsumer

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Windows;

namespace DelegateEvent
{
    public class WeakConsumer:IWeakEventListener
    {
        private string name;

        public WeakConsumer(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;
        }


    }
}

主方法：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace DelegateEvent
{
    class Program
    {
        static void Main(string[] args)
        {
            //var dealer = new CarDealer();
            //var michael = new Consumer("A"); //订阅者A
            //dealer.NewCarInfo += michael.NewCarIsHere;
            //dealer.NewCar("A_Car"); //A车到达 A得到通知

            //var sebastian = new Consumer("B"); //订阅者B
            //dealer.NewCarInfo += sebastian.NewCarIsHere;
            //dealer.NewCar("B_Car"); //B车到达 A、B都得到通知

            //dealer.NewCarInfo -= michael.NewCarIsHere; //A取消订阅
            //dealer.NewCar("C_Car"); //C车到达 只有B得到通知

            #region WeakEvent
            var dealer = new CarDealer();
            var michael = new WeakConsumer("A"); //订阅者A
            WeakCarInfoEventManager.AddListener(dealer,michael);
            dealer.NewCar("A_Car");

            var sebastian = new WeakConsumer("B"); //订阅者B
            WeakCarInfoEventManager.AddListener(dealer, sebastian);
            dealer.NewCar("B_Car"); //B车到达 A、B都得到通知

            WeakCarInfoEventManager.RemoveListener(dealer, michael);
            dealer.NewCar("C_Car");
            #endregion
        }
    }
}

CarDealer类 事件发布程序 不做任何更改

测试结果一致

事件发布程序和事件监听程序不再强连接