C#事件总线

简介

事件总线是对发布-订阅模式的一种实现,是一种集中式事件处理机制,允许不同的组件之间进行彼此通信而又不需要相互依赖,达到一种解耦的目的。

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
    {
        get
        {
            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);
    }
}

实际使用

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

总结

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!

参考资料

c# – 使用反射来发现派生类型
Prism.Core/Events/EventBase.cs
C# 事件总线 EventBus

posted @ 2021-05-11 23:46  time-flies  阅读(1334)  评论(12编辑  收藏  举报
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