实现事件总线

EventBus维护一个事件的字典，发布者、订阅者在事件总线中获取事件实例并执行发布、订阅操作，事件实例负责维护、执行事件处理程序。流程如下：
定义事件基类

事件实例需要在事件总线中注册，定义一个基类方便事件总线进行管理，代码如下：
/// <summary>
/// 事件基类
/// </summary>
public abstract class EventBase{ }
事件实例需要管理、执行已经注册的事件处理程序，为了适应不同的事件参数使用泛型参数，不允许此类实例化。代码如下：
/// <summary>
/// 泛型事件
/// </summary>
/// <typeparam name="T"></typeparam>
public abstract class PubSubEvent<T> : EventBase where T : EventArgs
    protected static readonly object locker = new object();
    protected readonly List<Action<object, T>> subscriptions = new List<Action<object, T>>();
    public void Subscribe(Action<object, T> eventHandler)
        lock (locker)
            if (!subscriptions.Contains(eventHandler))
                subscriptions.Add(eventHandler);
    public void Unsubscribe(Action<object, T> eventHandler)
        lock (locker)
            if (subscriptions.Contains(eventHandler))
                subscriptions.Remove(eventHandler);
    public virtual void Publish(object sender, T eventArgs)
        lock (locker)
            for (int i = 0; i < subscriptions.Count; i++)
                subscriptions[i](sender, eventArgs);
定义事件参数基类
事件参数基类继承EventArgs，使用泛型参数适应不同的参数类型，不允许此类实例化。代码如下：
/// <summary>
/// 泛型事件参数
/// </summary>
/// <typeparam name="T"></typeparam>
public abstract class PubSubEventArgs<T> : EventArgs
    public T Value { get; set; }
定义EventBus
EventBus只提供事件实例的管理，具体事件处理程序的执行由事件实例自己负责。为了使用方便，构造函数有自动注册事件的功能，在有多个程序集时可能会有bug。代码如下：
/// <summary>
/// 事件总线
/// </summary>
class EventBus
    private static EventBus _default;
    private static readonly object locker = new object();
    private Dictionary<Type, EventBase> eventDic = new Dictionary<Type, EventBase>();
    /// <summary>
    /// 默认事件总线实例，建议只使用此实例
    /// </summary>
    public static EventBus Default
            if (_default == null)
                lock (locker)
                    // 如果类的实例不存在则创建，否则直接返回
                    if (_default == null)
                        _default = new EventBus();                            
            return _default;
    /// <summary>
    /// 构造函数，自动加载EventBase的派生类实现
    /// </summary>
    public EventBus() 
        Type type = typeof(EventBase);
        Type typePubSub = typeof(PubSubEvent<>);
        Assembly assembly = Assembly.GetAssembly(type);
        List<Type> typeList = assembly.GetTypes()
            .Where(t => t != type && t != typePubSub && type.IsAssignableFrom(t))
            .ToList();
        foreach (var item in typeList)
            EventBase eventBase = (EventBase)assembly.CreateInstance(item.FullName);
            eventDic.Add(item, eventBase);
    /// <summary>
    /// 获取事件实例
    /// </summary>
    /// <typeparam name="TEvent">事件类型</typeparam>
    /// <returns></returns>
    public TEvent GetEvent<TEvent>() where TEvent : EventBase
        return (TEvent)eventDic[typeof(TEvent)];
    /// <summary>
    /// 添加事件类型
    /// </summary>
    /// <typeparam name="TEvent"></typeparam>
    public void AddEvent<TEvent>() where TEvent : EventBase ,new()
        lock (locker) 
            Type type = typeof(TEvent);
            if (!eventDic.ContainsKey(type))
                eventDic.Add(type, new TEvent());                    
    /// <summary>
    /// 移除事件类型
    /// </summary>
    /// <typeparam name="TEvent"></typeparam>
    public void RemoveEvent<TEvent>() where TEvent : EventBase, new()
        lock (locker)
            Type type = typeof(TEvent);
            if (eventDic.ContainsKey(type))
                eventDic.Remove(type);
使用事件总线
事件及事件参数
使用事件总线前，需要定义好事件及事件参数。在使用时，发布者、订阅者也必须知道事件类型及事件参数类型。代码如下：
/// <summary>
/// 泛型事件实现-TestAEvent，重写事件的触发逻辑
/// </summary>
public class TestAEvent: PubSubEvent<TestAEventArgs> 
    public override void Publish(object sender, TestAEventArgs eventArgs)
        lock (locker)
            for (int i = 0; i < subscriptions.Count; i++)
                var action= subscriptions[i];
                Task.Run(() => action(sender, eventArgs));
/// <summary>
/// 泛型事件参数实现-TestAEventArgs
/// </summary>
public class TestAEventArgs : PubSubEventArgs<string> { }
/// <summary>
/// 泛型事件实现-TestBEvent
/// </summary>
public class TestBEvent : PubSubEvent<TestBEventArgs> { }
/// <summary>
/// 泛型事件参数实现-TestBEventArgs
/// </summary>
public class TestBEventArgs : PubSubEventArgs<int> { }
注：TestAEvent中重写了事件发布的逻辑，每个事件在任务中执行。
定义发布者
发布者通过事件总线获取事件实例，在实例上发布事件，代码如下：
class Publisher
    public void PublishTeatAEvent(string value) 
        EventBus.Default.GetEvent<TestAEvent>().Publish(this, new TestAEventArgs() { Value=value});
    public void PublishTeatBEvent(int value)
        EventBus.Default.GetEvent<TestBEvent>().Publish(this, new TestBEventArgs() { Value = value });
定义订阅者
订阅者通过事件总线获取事件实例，在实例上订阅事件，代码如下：
class ScbscriberA
    public string Name { get; set; }
    public ScbscriberA(string name)
        Name = name;
        EventBus.Default.GetEvent<TestAEvent>().Subscribe(TeatAEventHandler);
    public void TeatAEventHandler(object sender, TestAEventArgs e)
        Console.WriteLine(Name+":"+e.Value);
class ScbscriberB
    public string Name { get; set; }
    public ScbscriberB(string name)
        Name = name;
        EventBus.Default.GetEvent<TestBEvent>().Subscribe(TeatBEventHandler);
    public void Unsubscribe_TeatBEvent() 
        EventBus.Default.GetEvent<TestBEvent>().Unsubscribe(TeatBEventHandler);
    public void TeatBEventHandler(object sender, TestBEventArgs e)
        Console.WriteLine(Name + ":" + e.Value);
代码如下：
class Program
    static void Main(string[] args)
        Publisher publisher = new Publisher();
        ScbscriberA scbscriberA = new ScbscriberA("scbscriberA");
        ScbscriberB scbscriberB1 = new ScbscriberB("scbscriberB1");
        ScbscriberB scbscriberB2 = new ScbscriberB("scbscriberB2");
        publisher.PublishTeatAEvent("test");
        publisher.PublishTeatBEvent(123);
        scbscriberB2.Unsubscribe_TeatBEvent();
        publisher.PublishTeatBEvent(12345);
        Console.ReadKey();           
运行结果：
scbscriberB1:123
scbscriberB2:123
scbscriberA:test
scbscriberB1:12345
这个事件总线只提供了基础功能，实现的发布者和订阅者的解耦，发布者、订阅者只依赖事件不互相依赖。

感觉我对事件总线的理解还有点不足，欢迎大家来一起讨论！
c# – 使用反射来发现派生类型

Prism.Core/Events/EventBase.cs

C# 事件总线 EventBus