runemoennike / lightmessagebus

What is LightMessageBus?

A simple, light-weight application level event aggregator which facilitates the exchange of messages between objects without direct references.

Use-cases and examples?

A soundComponent needs to be notified whenever a user clicks on any button.

MessageBus.Default.FromAny().Where<ButtonClickMessage>().Notify(soundComponent)

A taxCalculator needs to be notified whenever shopping cart is changed.

MessageBus.Default.From(shoppingCart).Notify(taxCalculator);

How is this achieved?

LightMessageBus uses a simple publisher/subscriber pattern.

• Subscribers use the MessageBus to subscribe to messages they wish to be notified about. They may wish to filter messages by the source, type of message or some other predicate.
• Publishers use the MessageBus to publish messages to the potential subscribers
• Neither subscribers nor publishers have any references to each other. They simply use a common communication channel - the MessageBus

How does that help?

The pub/sub pattern enables you to promote decoupled architecture in your application. Since there is no need for various objects (views, models, controllers, ...) to know of each other existence - you are free to develop them independently in isolation. Such architecture enables testing, refactoring and limits the propagation of changes through the system.

Why not use delegates/events?

Using delegates and/or events requires a reference between the publisher and the subscriber (subscribers reference publishers or vice-versa). Any change to the referenced class will affect the other. Such change may even propagate through the system resulting in significant changes due to a small cause.

How is it used?

LightMessageBus uses LINQ-like, fluent syntax for maximum readability and flexibility. The basic building blocks of a LightMessageBus registration expression are: From, Where and Notify.

First we define the publishers:

• From - specifies publisher(s) of interest to subscriber.
• FromAny - specifies any publisher.

Next we optionally define the messages:

• Where - specifies the types of messages of interest to subscriber.

Lastly we define the subscriber:

• Notify - specifies the subscriber.