ABP文档笔记 - 事件BUS

文档：

• ABP框架 - 领域事件（EventBus）
• EventBus & Domain Events
• ABP源码分析二十五：EventBus

EventBus（事件总线）

EventBus是一个单例对象，被所有类触发事件或处理事件时共享。

IEventBusConfiguration在应用启动时加载（by AbpCoreInstaller），依据它的配置决定 是所有IWindsorContainer实例共享同一条事件总线（EventBus.Default），还是每个IWindsorContainer实例创建一个自己的单例。默认使用EventBus.Default。

因为在应用中IocManager使用单例，IIocManager.IocContainer也是单一的，所以事件总线使用的就是EventBus.Default。

注入 IEventBus

使用属性注入模式：

public class TaskAppService : ApplicationService
{
    public IEventBus EventBus { get; set; }

    public TaskAppService()
    {
        EventBus = NullEventBus.Instance;
    }
}

直接使用默认实例

如果你不能注入它，可以直接使用EventBus.Default。使用方式如下所示：

EventBus.Default.Trigger(...); //trigger an event

但就如同不推荐使用IocManager.Instance一样，在任何可能的地方都不建议直接使用EventBus.Default，因为它难于单元测试。

定义事件

事件定义，继承EventData

在触发一个事件前，你首先要定义它，通过一个继承自EventData的类来表现一个事件。

假设当一个任务完成后我们想触发一个事件：

public class TaskCompletedEventData : EventData
{
    public int TaskId { get; set; }
}

这个类包含处理事件类所需要的属性，EventData类定义了EventSource（事件源，哪个对象触发了事件）和EventTime（何时触发的）属性。

泛型的事件定义，使用IEventDataWithInheritableGenericArgument

public class EntityEventData<TEntity> : EventData , IEventDataWithInheritableGenericArgument
{
    /// <summary>
    /// Related entity with this event.
    /// </summary>
    public TEntity Entity { get; private set; }

    /// <summary>
    /// Constructor.
    /// </summary>
    /// <param name="entity">Related entity with this event</param>
    public EntityEventData(TEntity entity)
    {
        Entity = entity;
    }

    public virtual object[] GetConstructorArgs()
    {
        return new object[] { Entity };
    }
}

ABP框架预定义的事件

异常处理事件

命名空间Event.Bus.Exceptions中定义了ExceptionData 和 AbpHandledExceptionData，当ABP自动处理任何异常时，会触发后者。

实体修改事件

命名空间Abp.Events.Bus.Entities中为实体修改提供了泛型的事件：EntityCreationEventData、EntityCreatedEventData、EntityUpdatingEventData、EntityUpdateEventData、EntityDeletingEventData和EntityDeletedEventData，同样也有EntityChangingEventData和EntityChangedEventData。

“ing”事件（例如EntityUpdating）在保存修改（SaveChanges）前触发，所以你可以在这些事件里，通过抛出异常，促使工作单元回滚，阻止操作）。“ed”事件（例如EntityUpdated）在保存修改之后被触发，也就没有机会让工作单元回滚了。

触发事件

简单例子

public class TaskAppService : ApplicationService
{
	public IEventBus EventBus { get; set; }

	public TaskAppService()
	{
		EventBus = NullEventBus.Instance;
	}

	public void CompleteTask(CompleteTaskInput input)
	{
		//TODO: complete the task on database...
		EventBus.Trigger(new TaskCompletedEventData {TaskId = 42});
	}
}

Trigger方法有几个重载：

EventBus.Trigger<TaskCompletedEventData>(new TaskCompletedEventData { TaskId = 42 }); //Explicitly declare generic argument
EventBus.Trigger(this, new TaskCompletedEventData { TaskId = 42 }); //Set 'event source' as 'this'
EventBus.Trigger(typeof(TaskCompletedEventData), this, new TaskCompletedEventData { TaskId = 42 }); //Call non-generic version (first argument is the type of the event class)

实体修改时事件的触发

在插入、更新或删除实体时，它们被ABP自动触发。如果你有一个Person实体，你可以注册EntityCreatedEventData，当一个新的Person创建并插入到数据库后，就可以收到通知。这些事件也支持继承，如果你有一个继承自Person的Student类，并且注册了EntityCreatedEventData，当一个Person或Student被插入后，你也会收到通知。

参阅 ABP框架 - 实体 ,使用AggregateRoot类的DomainEvents集合。

1. AbpDbContext in Abp.EntityFramework

    public override async Task<int> SaveChangesAsync(CancellationToken cancellationToken)
    {
        try
        {
            var changeReport = ApplyAbpConcepts();
            var result = await base.SaveChangesAsync(cancellationToken);
            await EntityChangeEventHelper.TriggerEventsAsync(changeReport);
            return result;
        }
        catch (DbEntityValidationException ex)
        {
            LogDbEntityValidationException(ex);
            throw;
        }
    }
   
    protected virtual EntityChangeReport ApplyAbpConcepts()
    {
        var changeReport = new EntityChangeReport();
   
        var userId = GetAuditUserId();
   
        var entries = ChangeTracker.Entries().ToList();
        foreach (var entry in entries)
        {
            switch (entry.State)
            {
                case EntityState.Added:
                    CheckAndSetId(entry.Entity);
                    CheckAndSetMustHaveTenantIdProperty(entry.Entity);
                    CheckAndSetMayHaveTenantIdProperty(entry.Entity);
                    SetCreationAuditProperties(entry.Entity, userId);
                    changeReport.ChangedEntities.Add(new EntityChangeEntry(entry.Entity, EntityChangeType.Created));
                    break;
                case EntityState.Modified:
                    SetModificationAuditProperties(entry, userId);
                    if (entry.Entity is ISoftDelete && entry.Entity.As<ISoftDelete>().IsDeleted)
                    {
                        SetDeletionAuditProperties(entry.Entity, userId);
                        changeReport.ChangedEntities.Add(new EntityChangeEntry(entry.Entity, EntityChangeType.Deleted));
                    }
                    else
                    {
                        changeReport.ChangedEntities.Add(new EntityChangeEntry(entry.Entity, EntityChangeType.Updated));
                    }
   
                    break;
                case EntityState.Deleted:
                    CancelDeletionForSoftDelete(entry);
                    SetDeletionAuditProperties(entry.Entity, userId);
                    changeReport.ChangedEntities.Add(new EntityChangeEntry(entry.Entity, EntityChangeType.Deleted));
                    break;
            }
   
            AddDomainEvents(changeReport.DomainEvents, entry.Entity);
        }
   
        return changeReport;
    }
   
    protected virtual void AddDomainEvents(List<DomainEventEntry> domainEvents, object entityAsObj)
    {
        var generatesDomainEventsEntity = entityAsObj as IGeneratesDomainEvents;
        if (generatesDomainEventsEntity == null)
        {
            return;
        }
   
        if (generatesDomainEventsEntity.DomainEvents.IsNullOrEmpty())
        {
            return;
        }
   
        domainEvents.AddRange(generatesDomainEventsEntity.DomainEvents.Select(eventData => new DomainEventEntry(entityAsObj, eventData)));
        generatesDomainEventsEntity.DomainEvents.Clear();
    }
   

2. EntityChangeEventHelper in Abp.Events.Bus.Entities

    public class EntityChangeEventHelper : ITransientDependency, IEntityChangeEventHelper
    {
    	public IEventBus EventBus { get; set; }
   
    	private readonly IUnitOfWorkManager _unitOfWorkManager;
   
    	public EntityChangeEventHelper(IUnitOfWorkManager unitOfWorkManager)
    	{
    		_unitOfWorkManager = unitOfWorkManager;
    		EventBus = NullEventBus.Instance;
    	}
   
    	public virtual void TriggerEvents(EntityChangeReport changeReport)
    	{
    		TriggerEventsInternal(changeReport);
   
    		if (changeReport.IsEmpty() || _unitOfWorkManager.Current == null)
    		{
    			return;
    		}
   
    		_unitOfWorkManager.Current.SaveChanges();
    	}
   
    	public Task TriggerEventsAsync(EntityChangeReport changeReport)
    	{
    		TriggerEventsInternal(changeReport);
   
    		if (changeReport.IsEmpty() || _unitOfWorkManager.Current == null)
    		{
    			return Task.FromResult(0);
    		}
   
    		return _unitOfWorkManager.Current.SaveChangesAsync();
    	}
   
    	public virtual void TriggerEntityCreatingEvent(object entity)
    	{
    		TriggerEventWithEntity(typeof(EntityCreatingEventData<>), entity, true);
    	}
   
    	public virtual void TriggerEntityCreatedEventOnUowCompleted(object entity)
    	{
    		TriggerEventWithEntity(typeof(EntityCreatedEventData<>), entity, false);
    	}
   
    	public virtual void TriggerEntityUpdatingEvent(object entity)
    	{
    		TriggerEventWithEntity(typeof(EntityUpdatingEventData<>), entity, true);
    	}
   
    	public virtual void TriggerEntityUpdatedEventOnUowCompleted(object entity)
    	{
    		TriggerEventWithEntity(typeof(EntityUpdatedEventData<>), entity, false);
    	}
   
    	public virtual void TriggerEntityDeletingEvent(object entity)
    	{
    		TriggerEventWithEntity(typeof(EntityDeletingEventData<>), entity, true);
    	}
   
    	public virtual void TriggerEntityDeletedEventOnUowCompleted(object entity)
    	{
    		TriggerEventWithEntity(typeof(EntityDeletedEventData<>), entity, false);
    	}
   
    	public virtual void TriggerEventsInternal(EntityChangeReport changeReport)
    	{
    		TriggerEntityChangeEvents(changeReport.ChangedEntities);
    		TriggerDomainEvents(changeReport.DomainEvents);
    	}
   
    	protected virtual void TriggerEntityChangeEvents(List<EntityChangeEntry> changedEntities)
    	{
    		foreach (var changedEntity in changedEntities)
    		{
    			switch (changedEntity.ChangeType)
    			{
    				case EntityChangeType.Created:
    					TriggerEntityCreatingEvent(changedEntity.Entity);
    					TriggerEntityCreatedEventOnUowCompleted(changedEntity.Entity);
    					break;
    				case EntityChangeType.Updated:
    					TriggerEntityUpdatingEvent(changedEntity.Entity);
    					TriggerEntityUpdatedEventOnUowCompleted(changedEntity.Entity);
    					break;
    				case EntityChangeType.Deleted:
    					TriggerEntityDeletingEvent(changedEntity.Entity);
    					TriggerEntityDeletedEventOnUowCompleted(changedEntity.Entity);
    					break;
    				default:
    					throw new AbpException("Unknown EntityChangeType: " + changedEntity.ChangeType);
    			}
    		}
    	}
   
    	protected virtual void TriggerDomainEvents(List<DomainEventEntry> domainEvents)
    	{
    		foreach (var domainEvent in domainEvents)
    		{
    			EventBus.Trigger(domainEvent.EventData.GetType(), domainEvent.SourceEntity, domainEvent.EventData);
    		}
    	}
   
    	protected virtual void TriggerEventWithEntity(Type genericEventType, object entity, bool triggerInCurrentUnitOfWork)
    	{
    		var entityType = entity.GetType();
    		var eventType = genericEventType.MakeGenericType(entityType);
   
    		if (triggerInCurrentUnitOfWork || _unitOfWorkManager.Current == null)
    		{
    			EventBus.Trigger(eventType, (IEventData)Activator.CreateInstance(eventType, new[] { entity }));
    			return;
    		}
   
    		_unitOfWorkManager.Current.Completed += (sender, args) => EventBus.Trigger(eventType, (IEventData)Activator.CreateInstance(eventType, new[] { entity }));
    	}
    }
   

事件的处理

处理一个事件，只要提供一个实现IEventHandler接口的类就可以了。

public class ActivityWriter : IEventHandler<TaskCompletedEventData>, ITransientDependency
{
	public void HandleEvent(TaskCompletedEventData eventData)
	{
		WriteActivity("A task is completed by id = " + eventData.TaskId);
	}
}

处理程序的自动注册

上例因为实现了ITransientDependency，它会被注册到Ioc容器，而ABP也会自动把它们注册到事件总线，当一个事件发生，ABP使用Ioc容器得到处理程序的引用，并在事件处理后释放该引用。在ABP里，这是使用事件总线的推荐的方式。

internal class EventBusInstaller : IWindsorInstaller
{
	//……
    public void Install(IWindsorContainer container, IConfigurationStore store)
    {
        if (_eventBusConfiguration.UseDefaultEventBus)
        {
            container.Register(
                Component.For<IEventBus>().UsingFactoryMethod(() => EventBus.Default).LifestyleSingleton()
                );
        }
        else
        {
            container.Register(
                Component.For<IEventBus>().ImplementedBy<EventBus>().LifestyleSingleton()
                );
        }

        _eventBus = container.Resolve<IEventBus>();
        container.Kernel.ComponentRegistered += Kernel_ComponentRegistered;
    }

    private void Kernel_ComponentRegistered(string key, IHandler handler)
    {
        if (!typeof(IEventHandler).IsAssignableFrom(handler.ComponentModel.Implementation))
        {
            return;
        }

        var interfaces = handler.ComponentModel.Implementation.GetInterfaces();
        foreach (var @interface in interfaces)
        {
            if (!typeof(IEventHandler).IsAssignableFrom(@interface))
            {
                continue;
            }

            var genericArgs = @interface.GetGenericArguments();
            if (genericArgs.Length == 1)
            {
                _eventBus.Register(genericArgs[0], new IocHandlerFactory(_iocResolver, handler.ComponentModel.Implementation));
            }
        }
    }
}

public class IocHandlerFactory : IEventHandlerFactory
{
    public Type HandlerType { get; private set; }
    private readonly IIocResolver _iocResolver;
    public IocHandlerFactory(IIocResolver iocResolver, Type handlerType)
    {
        _iocResolver = iocResolver;
        HandlerType = handlerType;
    }

    public IEventHandler GetHandler()
    {
        return (IEventHandler)_iocResolver.Resolve(HandlerType);
    }
    public void ReleaseHandler(IEventHandler handler)
    {
        _iocResolver.Release(handler);
    }
}

手动注册

public class EventBus : IEventBus
{
    /// <inheritdoc/>
    public IDisposable Register<TEventData>(Action<TEventData> action) where TEventData : IEventData
    {
        return Register(typeof(TEventData), new ActionEventHandler<TEventData>(action));
    }
    /// <inheritdoc/>
    public IDisposable Register<TEventData>(IEventHandler<TEventData> handler) where TEventData : IEventData
    {
        return Register(typeof(TEventData), handler);
    }
    /// <inheritdoc/>
    public IDisposable Register<TEventData, THandler>()
        where TEventData : IEventData
        where THandler : IEventHandler<TEventData>, new()
    {
        return Register(typeof(TEventData), new TransientEventHandlerFactory<THandler>());
    }
    /// <inheritdoc/>
    public IDisposable Register(Type eventType, IEventHandler handler)
    {
        return Register(eventType, new SingleInstanceHandlerFactory(handler));
    }
    /// <inheritdoc/>
    public IDisposable Register<TEventData>(IEventHandlerFactory handlerFactory) where TEventData : IEventData
    {
        return Register(typeof(TEventData), handlerFactory);
    }
    /// <inheritdoc/>
    public IDisposable Register(Type eventType, IEventHandlerFactory handlerFactory)
    {
        GetOrCreateHandlerFactories(eventType)
            .Locking(factories => factories.Add(handlerFactory));

        return new FactoryUnregistrar(this, eventType, handlerFactory);
    }

事件总线的Register方法有几个重载，也就提供了多种注册方式。

接受一个委托

EventBus.Register<TaskCompletedEventData>(eventData =>
{
    WriteActivity("A task is completed by id = " + eventData.TaskId);
});

处理程序

internal class ActionEventHandler<TEventData> :
    IEventHandler<TEventData>,
    ITransientDependency
{
    /// <summary>
    /// Action to handle the event.
    /// </summary>
    public Action<TEventData> Action { get; private set; }

    /// <summary>
    /// Creates a new instance of <see cref="ActionEventHandler{TEventData}"/>.
    /// </summary>
    /// <param name="handler">Action to handle the event</param>
    public ActionEventHandler(Action<TEventData> handler)
    {
        Action = handler;
    }

    /// <summary>
    /// Handles the event.
    /// </summary>
    /// <param name="eventData"></param>
    public void HandleEvent(TEventData eventData)
    {
        Action(eventData);
    }
}

接受一个实现了IEventHantler的对象

EventBus.Register<TaskCompletedEventData>(new ActivityWriter());

注册为一个SingleInstanceHandlerFactory

internal class SingleInstanceHandlerFactory : IEventHandlerFactory
{

    public IEventHandler HandlerInstance { get; private set; }

    public SingleInstanceHandlerFactory(IEventHandler handler)
    {
        HandlerInstance = handler;
    }

    public IEventHandler GetHandler()
    {
        return HandlerInstance;
    }

    public void ReleaseHandler(IEventHandler handler)
    {

    }
}

接受两个泛型参数

EventBus.Register<TaskCompletedEventData, ActivityWriter>();

注册为一个TransientEventHandlerFactory

internal class TransientEventHandlerFactory<THandler> : IEventHandlerFactory
    where THandler : IEventHandler, new()
{
    public IEventHandler GetHandler()
    {
        return new THandler();
    }
    public void ReleaseHandler(IEventHandler handler)
    {
        if (handler is IDisposable)
        {
            (handler as IDisposable).Dispose();
        }
    }
}

直接注册一个IEventHandlerFactory

上面的几种注册方式，最终都是在间接调用下面这个方法

    public IDisposable Register(Type eventType, IEventHandlerFactory handlerFactory)
    {
        GetOrCreateHandlerFactories(eventType)
            .Locking(factories => factories.Add(handlerFactory));

        return new FactoryUnregistrar(this, eventType, handlerFactory);
    }

事件处理的取消注册

1. 最简单的方式就是释放Register方法返回的值

    //Register to an event...
    var registration = EventBus.Register<TaskCompletedEventData>(eventData => WriteActivity("A task is completed by id = " + eventData.TaskId) );
    //Unregister from event
    registration.Dispose();
   

2. Unregister方法

    //Create a handler
    var handler = new ActivityWriter();
   
    //Register to the event
    EventBus.Register<TaskCompletedEventData>(handler);
   
    //Unregister from event
    EventBus.Unregister<TaskCompletedEventData>(handler);
   

3. EventBus提供了一个UnregisterAll()方法，它反注册一个事件的所有处理程序

4. UnregisterAll()方法反注册所有事件的所有处理程序。