单体程序的事件发布/订阅（EventBus）

成员介绍：

IEventBus、EventBus：事件总线

IEventHandler、xxxEventHandler：事件处理程序

IEvent、xxxEvent：事件，一个事件可对应多个事件处理程序

EventHandlerAttribute：事件处理程序的特性，可添加排序信息等

EvnetHandlerMetadata：IEventHandler信息

EventHandlerMetadataItem：EventHandler实例信息

事件总线：

    public interface IEventBus
    {
        void Trigger<TEvent>(TEvent eventData, string topic = null) where TEvent : IEvent;
    }
    public class EventBus : IEventBus
    {
        private static System.Collections.Concurrent.ConcurrentDictionary<Type, EvnetHandlerMetadata> _evnetHandlerMetadatas
            = new ConcurrentDictionary<Type, EvnetHandlerMetadata>();
        private static readonly EventHandlerAttribute DefaultAttribute = new EventHandlerAttribute()
        {
            IgnoreError = false,
            Priority = 0,
            Topic = null
        };

        static EventBus()
        { }


        public Func<Type, object> Activator { get; set; }

        /// <summary>
        /// 触发事件
        /// </summary>
        /// <typeparam name="IEvent"></typeparam>
        /// <param name="eventData"></param>
        public void Trigger<TEvent>(TEvent eventData, string topic = null) where TEvent : IEvent
        {

            EvnetHandlerMetadata evnetHandlerMetadata = _evnetHandlerMetadatas.GetOrAdd(typeof(TEvent), (key) =>
            {
                var handlerType = typeof(IEventHandler<>).MakeGenericType(typeof(TEvent));
                var handlerMetadata = new EvnetHandlerMetadata()
                {
                    EventHandlerType = handlerType,
                    EventType = key,
                    Items = new List<EventHandlerMetadataItem>()
                };
                var handlerInstances = Activator.Invoke(typeof(IEnumerable<>).MakeGenericType(handlerType)) as IEnumerable;
                foreach (var handlerInstance in handlerInstances)
                {
                    var typeInfo = handlerInstance.GetType().GetTypeInfo();
                    var handleMethods = typeInfo.DeclaredMethods.Where(t => t.Name.EndsWith($"{key.Name}>.Handle") || t.Name == "Handle");
                    var method = handleMethods.FirstOrDefault();
                    if (method == null) continue;
                    var attr = method.GetCustomAttribute<EventHandlerAttribute>()
                        ?? handlerInstance.GetType().GetCustomAttribute<EventHandlerAttribute>()
                        ?? DefaultAttribute
                        ;
                    handlerMetadata.Items.Add(new EventHandlerMetadataItem()
                    {
                        Method = method,
                        IgnoreError = attr.IgnoreError,
                        Priority = attr.Priority,
                        Type = handlerInstance.GetType()
                    });
                }
                handlerMetadata.Items = handlerMetadata.Items.OrderByDescending(p => p.Priority).ThenBy(x => x.Type.Name).ToList();
                return handlerMetadata;
            });

            var handlers = evnetHandlerMetadata.Items
                .WhereIf(p => p.Topic == topic, !string.IsNullOrEmpty(topic))
                .Select(x => new { Instance = Activator.Invoke(x.Type), Meta = x })
                .ToList()
                ;
            foreach (var handler in handlers)
            {
                try
                {
                    handler.Meta.Method.Invoke(handler.Instance, new object[] { eventData });
                }
                catch (Exception ex)
                {
                    if (!handler.Meta.IgnoreError)
                    {
                        while (true)
                        {
                            if (ex.InnerException == null)
                            {
                                throw ex;
                            }
                            else
                            {
                                ex = ex.InnerException;
                            }
                        }

                    }
                }
            }
        }

        public class EventHandlerMetadataItem
        {
            public Type Type { get; set; }
            public MethodInfo Method { get; set; }
            public int Priority { get; set; }
            public bool IgnoreError { get; set; }
            public string Topic { get; set; }

        }

        public class EvnetHandlerMetadata
        {
            public List<EventHandlerMetadataItem> Items { get; set; }
            public Type EventHandlerType { get; set; }
            public Type EventType { get; set; }

        }
    }

事件处理接口：

    /// <summary>
    /// 事件处理接口
    /// </summary>
    /// <typeparam name="TEvent">继承IEvent对象的事件源对象</typeparam>
    public interface IEventHandler<T> where T : IEvent
    {
        /// <summary>
        /// 处理程序
        /// </summary>
        /// <param name="evt"></param>
        void Handle(T evt);
    }

    [AttributeUsage(AttributeTargets.Class | AttributeTargets.Method, AllowMultiple = false, Inherited = false)]
    public class EventHandlerAttribute : Attribute
    {
        /// <summary>
        /// 执行优先级
        /// </summary>
        public int Priority { get; set; }
        public bool IgnoreError { get; set; }
        public string Topic { get; set; }
        public EventHandlerAttribute()
        {

        }
    }

public interface IEvent
{
}

具体事件处理：

    /// <summary>
    /// 文件上传事件处理
    /// </summary>
    [EventHandler(Priority =1, IgnoreError = true)]
    public class FileUploadEventHandler : IEventHandler<FileUploadEvent>
    {
        private readonly IFeeService _feeService;
        private readonly ILogger _logger;

        public FileUploadEventHandler(
            IFeeService feeService,
            ILogger<FileUploadEventHandler> logger
            )
        {
            _feeService = feeService;
            _logger = logger;
        }

        public void Handle(FileUploadEvent evt)
        {
           // _logger.LogInformation(evt.FileName);
            ////扣减存储空间
            //var useResult=_feeService.UseFeeItem(Enums.Finance_FeeItem.Storage, evt.FileSize, $"上传文件{evt.FileName}");
            //if (!useResult.Success)
            //{
            //    throw new Exception(useResult.Message);
            //}
        }
    }

事件触发：

var eventBus = _serviceLocator.GetService<IEventBus>();
eventBus.Trigger(new FileUploadEvent() { OwnUserID = globalValue.User.ID, UserID = globalValue.User.OwnUserID, Url = uploadResult.Data.Url, FileName = file.FileName, FileSize = file.Length, FileType = fileType });

参考：https://www.cnblogs.com/lwqlun/p/10468058.html