ABP文档笔记 - 事件BUS

文档：

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 : EventData , IEventDataWithInheritableGenericArgument
{
///

/// Related entity with this event.
///

public TEntity Entity { get; private set; }

///

/// Constructor.
///

/// Related entity with this event
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(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。

AbpDbContext in Abp.EntityFramework

public override async Task 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().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 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();
}
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 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 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, 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().UsingFactoryMethod(() => EventBus.Default).LifestyleSingleton()
);
}
else
{
container.Register(
Component.For().ImplementedBy().LifestyleSingleton()
);
}

_eventBus = container.Resolve();
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
{
///
public IDisposable Register(Action action) where TEventData : IEventData
{
return Register(typeof(TEventData), new ActionEventHandler(action));
}
///
public IDisposable Register(IEventHandler handler) where TEventData : IEventData
{
return Register(typeof(TEventData), handler);
}
///
public IDisposable Register<TEventData, THandler>()
where TEventData : IEventData
where THandler : IEventHandler, new()
{
return Register(typeof(TEventData), new TransientEventHandlerFactory());
}
///
public IDisposable Register(Type eventType, IEventHandler handler)
{
return Register(eventType, new SingleInstanceHandlerFactory(handler));
}
///
public IDisposable Register(IEventHandlerFactory handlerFactory) where TEventData : IEventData
{
return Register(typeof(TEventData), handlerFactory);
}
///
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(eventData =>
{
WriteActivity("A task is completed by id = " + eventData.TaskId);
});

处理程序

internal class ActionEventHandler :
IEventHandler,
ITransientDependency
{
///

/// Action to handle the event.
///

public Action Action { get; private set; }

///

/// Creates a new instance of .
///

/// Action to handle the event
public ActionEventHandler(Action handler)
{
Action = handler;
}

///

/// Handles the event.
///

///
public void HandleEvent(TEventData eventData)
{
Action(eventData);
}
}

接受一个实现了IEventHantler的对象

EventBus.Register(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 : 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));