event-aggregation (C#)

A simple event aggreator, that eases subscription and publishing of typed events.

Same documentation for F# programmers

The main objectives for the library is to:

• Facilitate a simple event aggregator, to which:
  • Subscribers implementing either synchronous or asynchronous consumption can subscribe to published event
  • Publishers can out of band publish messages to subscribers
• Utilizing loose coupling. This is done by:
  • Having the event aggregator not holding on to subscribers. The event aggregator does this via weak references, such that subscribers can go away silently
  • Utilizing TPL dataflow action blocks to act as mail boxes for messages
• Let subscribers determine whether they want to receive messages in order or not. This is done be configuring the TPL dataflow action blocks' level of parallelism
• Let subscribers determine whether they want to be notified as direct calls or inside a provided SynchronizationContext

The library consists of:

• Three interfaces
• Two types implementing one of the interfaces and also IDisposable

classDiagram
IDisposable <|-- IEventAggregator
IEventAggregator <|-- EventAggregator
IDisposable <|-- Subscription

class IHandle {
    Handle(message: T)
}
class IHandleAsync {
    HandleAsync(message: T) : Task
}

class IEventAggregator {
    Subscribe(subscriber: IHandle, synchronizationContext: SynchronizationContext, serializeNotification: bool) : IDisposable
    SubscribeAsync(subscriber: IHandleAsync, synchronizationContext: SynchronizationContext, serializeNotification: bool) : IDisposable
    Publish(message: T)
}

class EventAggregator {
    Subscribe(subscriber: IHandle, synchronizationContext: SynchronizationContext, serializeNotification: bool) : Subscription
    SubscribeAsync(subscriber: IHandleAsync, synchronizationContext: SynchronizationContext, serializeNotification: bool) : Subscription
    Publish(message: T)
    Finalize()
}

The interfaces and some of the classes are actual generic on the type of message to publish via the event-aggregator:

• IHandle<T> is a generic interface with a single method:
  • Handle(message: T). This interface is implemented by subscribers who want to be notified with messages of type synchronously