.NET组件程序设计 第6章 事件

基于委托的事件：

发布事件的对象叫事件源（发布者），响应事件并处理的一方叫接受器（订阅者）。

事件通知形式：发布者调用订阅者的方法。

 

使用.NET事件：

//定义委托签名//参数sender：订阅者为多个发布者提供相同处理方法，为区分不同发布者用//参数eventArgs：提供给事件的特定参数容器对象，要防止其中定义属性被订阅者修改public delegate void MyEventHandler(object sender, EventArgs eventArgs);//.NET提供EventHandler委托public delegate void EventHandler(object sender, EventArgs eventArgs);public delegate void EventHandler<E>(object sender, E e)where E : EventArgs;

订阅者事件处理方法名规范为On+事件名称。

 

泛型事件处理：

//泛型委托签名public delegate void GenericEventHandler<T, U>(T t, U u);//也可以使用别名，但别名作用域不可超过该文件作用域//using MyHandler = GenericEventHandler<T, U>(T t, U u);//自定义事件参数类public class MyEventArgs : EventArgs{...}//事件发布者public class MyPublisher{ //定义类型安全的事件MyEvent public event GenericEventHandler<MyPublisher, MyEventArgs> MyEvent; //public event MyHandler MyEvent; public void FireEvent() { MyEventArgs args = new MyEventArgs(...); MyEvent(this, args); }}//类型安全的事件订阅者public class MySubscriber<A> where A ： EventArgs{ public void OnMyEvent(MyPublisher sender, A args) {...}}MyPublisher publisher = new MyPublisher();MySubscriber<MyEventArgs> subscriber = new MySubscriber<MyEventArgs>();publisher.MyEvent += subscriber.OnEvent;publisher.FireEvent();

 

防御式发布事件：

public class MyPublisher{ public event EventHandler MyEvent; //触发事件 public void FireEvent() { //安全发布事件，每次检查委托值是否为空 if(MyEvent == null) { return; } Delegate[] delegates = MyEvent.GetInvocationList(); foreach(Delegate del in delegates) { try { EventHandler sink = (EventHandler)del; sink(this, EventArgs.Empty); } catch{ ... } } }}

 

EventsHelper类安全可重用的触发事件：

public delegate void GenericEventHandler<T, U>(T t, U u);//事件发布者public class MyPublisher{ public event GenericEventHandler<MyPublisher, EventArgs> MyEvent; //安全发布事件 public void FireEvent() { EventsHelper.Fire(MyEvent, this, EventArgs.Empty); }}//EventsHelper安全可重用触发任何类型的事件public static class EventsHelper{ public static void Fire<T, U>(GenericEventHandler<T, U> del, T t, U u) { UnsafeFire(del, t, u); } //支持EventHandler<E>泛型 public static void Fire<E>(EventHandler<E> del, object sender, E e) where E : EventArgs { UnsafeFire(del, sender, e); } private static void UnsafeFire(Delegate del, params object[] args) { if (del == null) { return; } Delegate[] delegates = del.GetInvocationList(); foreach (Delegate sink in delegates) { try { sink.DynamicInvoke(args); } catch { } } }}

 

事件访问器：

//事件发布者public class MyPublisher{ //公开公共类成员违反封装，信息隐藏 //事件访问器类似于属性机制，易于使用同时隐藏实际类成员 private EventHandler m_MyEvent; public event EventHandler MyEvent { add { m_MyEvent += value; } remove { m_MyEvent -= value; } } //安全发布事件 public void FireEvent() { EventsHelper.Fire(m_MyEvent, this, EventArgs.Empty); }}

 

管理大量事件：

System.ComponentModel.EventHandlerList类，存储键值对的线性列表。

using System.ComponentModel;using MouseEventHandler = GenericEventHandler<MyButton, EventArgs>;public delegate void GenericEventHandler<T, U>(T t, U u);public class MyButton{ //私有委托列表 private EventHandlerList m_EventList; //预先分配静态键，使所有实例恭喜。避免每次调用都新建一字符串作为键，减轻托管堆压力 private static object m_MouseMoveEventKey = new object(); //定义一个事件 public event MouseEventHandler MouseMove { add { m_EventList.AddHandler(m_MouseMoveEventKey, value); } remove { m_EventList.RemoveHandler(m_MouseMoveEventKey, value); } } //构造函数 public MyButton() { m_EventList = new EventHandlerList(); } //触发事件 public void Fire() { MouseEventHandler handler = m_EventList[m_MouseMoveEventKey] as MouseEventHandler; //EventsHelper.Fire(handler, this, EventArgs.Empty); }}

 

编写接收器（订阅者）接口：

using MyEventHandler = GenericEventHandler<MyPublisher, EventArgs>;public delegate void GenericEventHandler<T, U>(T t, U u);//发布者public class MyPublisher{ MyEventHandler m_Event1; MyEventHandler m_Event2; MyEventHandler m_Event3; //订阅事件 public void Subscribe(IMySubscriber subscriber, EventType eventType) { if ((eventType & EventType.OnEvent1) == EventType.OnEvent1) { m_Event1 += subscriber.OnEvent1; } if ((eventType & EventType.OnEvent2) == EventType.OnEvent2) { m_Event2 += subscriber.OnEvent2; } if ((eventType & EventType.OnEvent3) == EventType.OnEvent3) { m_Event3 += subscriber.OnEvent3; } } //取消事件 public void UnSubscribe(IMySubscriber subscriber, EventType eventType) { if ((eventType & EventType.OnEvent1) == EventType.OnEvent1) { m_Event1 -= subscriber.OnEvent1; } if ((eventType & EventType.OnEvent2) == EventType.OnEvent2) { m_Event2 -= subscriber.OnEvent2; } if ((eventType & EventType.OnEvent3) == EventType.OnEvent3) { m_Event3 -= subscriber.OnEvent3; } } //触发事件 public void Fire(EventType eventType) { if ((eventType & EventType.OnEvent1) == EventType.OnEvent1) { //EventsHelper.Fire(m_Event1, this, EventArgs.Empty); } if ((eventType & EventType.OnEvent2) == EventType.OnEvent2) { //EventsHelper.Fire(m_Event2, this, EventArgs.Empty); } if ((eventType & EventType.OnEvent3) == EventType.OnEvent3) { //EventsHelper.Fire(m_Event3, this, EventArgs.Empty); } }}//事件类型枚举//Flags特性，表示当前枚举可以位运算[Flags]public enum EventType{ OnEvent1, OnEvent2, OnEvent3, OnAllEvents = OnEvent1 | OnEvent2 | OnEvent3}//接收器接口public interface IMySubscriber{ void OnEvent1(object sender, EventArgs args); void OnEvent2(object sender, EventArgs args); void OnEvent3(object sender, EventArgs args);}//订阅者public class MySubscriber : IMySubscriber{ #region IMySubscriber 成员 void IMySubscriber.OnEvent1(object sender, EventArgs args) { //throw new NotImplementedException(); } void IMySubscriber.OnEvent2(object sender, EventArgs args) { //throw new NotImplementedException(); } void IMySubscriber.OnEvent3(object sender, EventArgs args) { //throw new NotImplementedException(); } #endregion}/********** 调用 **********/MyPublisher publisher = new MyPublisher();IMySubscriber subscriber = new MySubscriber();//订阅事件1和事件2publisher.Subscribe(subscriber, EventType.OnEvent1 | EventType.OnEvent2);//仅仅触发事件1publisher.Fire(EventType.OnEvent1);