闲来无聊在我的Biwen.QuickApi中实现一下极简的事件总线,其实代码还是蛮简单的,对于初学者可能有些帮助 就贴出来,有什么不足的地方也欢迎板砖交流~ 。

首先定义一个事件约定的空接口 。

    public interface IEvent{}

然后定义事件订阅者接口 。

public interface IEventSubscriber<T> where T : IEvent
    {
        Task HandleAsync(T @event, CancellationToken ct);
        /// <summary>
        /// 执行排序
        /// </summary>
        int Order { get; }

        /// <summary>
        /// 如果发生错误是否抛出异常,将阻塞后续Handler
        /// </summary>
        bool ThrowIfError { get; }
    }
    public abstract class EventSubscriber<T> : IEventSubscriber<T> where T : IEvent
    {
        public abstract Task HandleAsync(T @event, CancellationToken ct);
        public virtual int Order => 0;
        /// <summary>
        /// 默认不抛出异常
        /// </summary>
        public virtual bool ThrowIfError => false;
    }

接着就是发布者 。

internal class Publisher(IServiceProvider serviceProvider)
{
	public async Task PublishAsync<T>(T @event, CancellationToken ct) where T : IEvent
	{
		var handlers = serviceProvider.GetServices<IEventSubscriber<T>>();
		if (handlers is null) return;
		foreach (var handler in handlers.OrderBy(x => x.Order))
		{
			try
			{
				await handler.HandleAsync(@event, ct);
			}
			catch
			{
				if (handler.ThrowIfError)
				{
					throw;
				}
				//todo:
			}
		}
	}
}

到此发布订阅的基本代码也就写完了.接下来就是注册发布者和所有的订阅者了 。

核心代码如下

        static readonly Type InterfaceEventSubscriber = typeof(IEventSubscriber<>);
        static readonly object _lock = new();//锁
        static bool IsToGenericInterface(this Type type, Type baseInterface)
        {
            if (type == null) return false;
            if (baseInterface == null) return false;
            return type.GetInterfaces().Any(x => x.IsGenericType && x.GetGenericTypeDefinition() == baseInterface);
        }
        static IEnumerable<Type> _eventHanlers = null!;
        static IEnumerable<Type> EventHandlers
        {
            get
            {
                lock (_lock)
                    return _eventHanlers ??= ASS.InAllRequiredAssemblies.Where(x =>
                    !x.IsAbstract && x.IsPublic && x.IsClass && x.IsToGenericInterface(InterfaceEventSubscriber));
            }
        }
		    //注册EventSubscribers
            foreach (var handlerType in EventHandlers)
            {
                var baseType = handlerType.GetInterfaces().First(x => x.IsGenericType && x.GetGenericTypeDefinition() == InterfaceEventSubscriber);
                services.AddScoped(baseType, handlerType);
            }
            //注册Publisher
            services.AddScoped<Publisher>();
		

至此发布订阅的代码也就完成了! 现在我们将发布订阅封装到QuickApi中使用

internal interface IPublisher
{
	/// <summary>
	/// Event Publish
	/// </summary>
	/// <typeparam name="T"></typeparam>
	/// <param name="event">Event</param>
	/// <returns></returns>
	Task PublishAsync<T>(T @event, CancellationToken cancellationToken) where T : IEvent;
}

然后BaseQuickApi实现IPublisher接口 。

internal interface IQuickApi<Req, Rsp> : IHandlerBuilder, IQuickApiMiddlewareHandler, IAntiforgeryApi, IPublisher
{
    ValueTask<Rsp> ExecuteAsync(Req request);
}

// BaseQuickApi.PublishAsync
public virtual async Task PublishAsync<T>(T @event, CancellationToken cancellationToken = default) where T : IEvent
{
    using var scope = ServiceRegistration.ServiceProvider.CreateScope();
    var publisher = scope.ServiceProvider.GetRequiredService<Publisher>();
    await publisher.PublishAsync(@event, cancellationToken);
}

至此功能完成,接下来我们测试一下

using Biwen.QuickApi.Events;
using Microsoft.AspNetCore.Mvc;

namespace Biwen.QuickApi.DemoWeb.Apis
{
    public class MyEvent : BaseRequest<MyEvent>,IEvent
    {
        [FromQuery]
        public string? Message { get; set; }
    }

    public class MyEventHandler : EventSubscriber<MyEvent>
    {
        private readonly ILogger<MyEventHandler> _logger;
        public MyEventHandler(ILogger<MyEventHandler> logger)
        {
            _logger = logger;
        }

        public override Task HandleAsync(MyEvent @event, CancellationToken ct)
        {
            _logger.LogInformation($"msg 2 : {@event.Message}");
            return Task.CompletedTask;
        }
    }

    /// <summary>
    /// 更早执行的Handler
    /// </summary>
    public class MyEventHandler2 : EventSubscriber<MyEvent>
    {
        private readonly ILogger<MyEventHandler2> _logger;
        public MyEventHandler2(ILogger<MyEventHandler2> logger)
        {
            _logger = logger;
        }

        public override Task HandleAsync(MyEvent @event, CancellationToken ct)
        {
            _logger.LogInformation($"msg 1 : {@event.Message}");
            return Task.CompletedTask;
        }

        public override int Order => -1;

    }

    /// <summary>
    /// 抛出异常的Handler
    /// </summary>
    public class MyEventHandler3 : EventSubscriber<MyEvent>
    {
        private readonly ILogger<MyEventHandler3> _logger;
        public MyEventHandler3(ILogger<MyEventHandler3> logger)
        {
            _logger = logger;
        }

        public override Task HandleAsync(MyEvent @event, CancellationToken ct)
        {
            throw new Exception("error");
        }

        public override int Order => -2;

        public override bool ThrowIfError => false;

    }

    [QuickApi("event")]
    public class EventApi : BaseQuickApi<MyEvent>
    {
        public override async ValueTask<IResultResponse> ExecuteAsync(MyEvent request)
        {
            //publish
            await PublishAsync(request);
            return IResultResponse.Content("send event");
        }
    }
}

最后我们运行项目测试一下功能

curl -X 'GET' \
  'http://localhost:5101/quick/event?Message=hello%20world' \
  -H 'accept: */*'

源代码我发布到了GitHub,欢迎star! https://github.com/vipwan/Biwen.QuickApi 。

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