EventBus

This is an EventBus which refered the ApplicationContext.publish(message), which is used to publish an Event in Java Spring.

Normally, EventHandler should be coupled with the Event directly, which is not a good pratice for multi-solution application. This lib provides another different use-case of the Event-Listener parttern: you can separate your EventHandler and Event into different solution or project, and the EventBus can dispatch the event to the corresponding EventHandlers.

What is a correspocorresponding EventHandler?

Suppose you have an event named BaseEvent, There is no doubt an EventHandler like the following code can be invoked by the EventBus

public class BaseHandler: IEventListener<BaseEvent>

Further for, if you have another Event which is an extend of BaseEvent, take the following code as an example:

public class FooEvent: BaseEvent

It is not only a FooEvent, but also a BaseEvent, so the EventListener above can handle it as well.

This is the characteristic of this library

1 Basic

1.1 Install

You can install it via nuget

• .NetFramework
• .NetCore

1.2 Runtime

• Reface.EventBus is working based on .NetFramework
• Reface.Core.EventBus is working based on .NetCore

1.3 Dependencies

Reface.EventBus

• Nothing

Reface.Core.EventBus

• Microsoft.Extensions.DependencyInjection

2 Usage

2.1 Publish a Message

Define a New Event

/// <summary>
/// This Event will be publish after the console started
/// </summary>
public class ConsoleStarted : Reface.EventBus.Event
{
    public ConsoleStarted(object source) : base(source)
    {
        Console.WriteLine("Console Started");
    }
}

Publish Event

class Program
{
    static void Main(string[] args)
    {
        // Create an instance of EventBus
        IEventBus eventBus = new DefaultEventBus();

        // Publish the message
        eventBus.Publish(new ConsoleStarted());
    }
}

2.2 Event Handler

2.2.1 How to listener an event

And class who implements the interface IEventListener<TEvent> would be an event listener.

using ConsoleApp1.Events;
using Reface.EventBus;

namespace ConsoleApp1.Listeners
{
    public class OnConsoleStarted : IEventListener<ConsoleStarted>
    {
        public void Handle(ConsoleStarted @event)
        {
            Console.WriteLine("Console Started");
        }
    }
}

2.2.2 How to register a Listener

In order to decouple the code, You can register the Listener in the config file

Register listener in web.config / app.config

1. add section
2. add listener

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <configSections>
    <section name="eventBus" type="Reface.EventBus.Configuration.EventBusSection, Reface.EventBus"/>
  </configSections>
  <eventBus>
    <listeners>
      <add type="ConsoleApp1.Listeners.OnConsoleStarted, ConsoleApp1" />
    </listeners>
  </eventBus>
</configuration>

2.2.3 其它方法添加监听者

除了通过 config 文件的方法，我们还提供了其它方法来注册监听者。

只要实现了 Reface.EventBus.IEventListenerFinder 并在构造 DefaultEventBus 时作为参数传入，便可以订制的方式注册监听者。 目前自带的注册方式有：

• Reface.EventBus.EventListenerFinders.ConfigurationEventListenerFinder 通过 config 文件来注册
• Reface.EventBus.EventListenerFinders.AssembliesEventListenerFinder 通过注册程序集，并返反射其中的类型来得到所有实现了 Reface.EventBus.IEventListenerFinder 的成员
• Reface.EventBus.EventListenerFinders.DefaultEventListenerFinder 通过编码的方式注册监听者

2.2.4 定义执行顺序

向 IEventListener 的实现类再添加 IPrioritized 接口，并实现 Priority 属性，便可以指定执行的顺序。

• Priority 的值越小，越先执行
• 未实现 IPrioritized 的 IEventListener 认为 Priority = 0

3. 集成

3.1 .NetCore 与 ServiceCollection 集成

与 IOC/DI 组件的集成，可以免去对监听者一一注册的过程。 在 .NetCore 中，通过为 ServiceCollection 注册必要组件和按程序集注册监听器，可以实现这些功能：

var provider = new ServiceCollection()
  .AddEventBus() // 添加 EventBus 功能
  .AddEventListeners(this.GetType().Assembly)
  .AddEventListeners(typeof(IService).Assembly)
  .BuildServiceProvider();
IEventBus eventBus = provider.GetService<IEventBus>();
eventBus.Publish(new TestEvent());