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Publish & Subscribe to events using an Event Aggregator
The document explains the publish-subscribe design pattern, which facilitates loose coupling between message publishers and subscribers through an event aggregator. It provides insights into implementing this pattern with code samples, demonstrating how to define, publish, and handle messages effectively. The approach aims to create maintainable and testable code, applicable in various software layers.
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Publish & Subscribe to events using an Event Aggregator
- 1. Publish- and Subscribeto events using an Event Aggregator Lars-Erik Kindblad Senior Consultant Blog: kindblad.com
- 2. Agenda What is thePublish-Subscribe Pattern? Message Publisher Subscriber Event Aggregator and how to create one Code Sample #1 and #2 without and with publish-subscribe Summary
- 3. What is thePublish-Subscribe Pattern? Publish-Subscribe = Pub/Sub Message/event based pattern The publisher creates and publishes messages through an event aggregator (message bus) – but don’t program the messages to be sent directly to any subscribers The subscribers define what messages they want to subscribe to Event Aggregator Subscriber Subscriber Publisher Message MessageMessage Subscribe
- 4. What is aMessage? A simple .NET POCO class with or without properties
- 5. What is aPublisher? Any class that wants to create and publish a message
- 6. What is aSubscriber? Any class that wants to do something when a specific message or event occurs
- 7. What is anEvent Aggregator? A lightweight message bus Accepts a message and publishes it out to only those who subscribes for it Can be synchronous or asynchronous Must have Publish(message) method Can have Subscribe(subscriber) method Unsubscribe(subscriber) method
- 8. Event Aggregator forthe UI
- 9. Event Aggregator fornon-UI
- 10.
- 11. Name: MainForm Name: NewCustomerControl Name:ToolbarControl
- 12. New requirement Save buttonshould be disabled when the first name or lastname is empty
- 14. NewCustomerControl ToolbarControl BtnSave.Enabled = true/false Dependencygraph Strongly Coupled Code
- 15. Control Control Control Control Control Control Control Control Dependencygraph for a more complex scenario Strongly Coupled Code
- 16. Dependency graph foran enterprise application Even more strongly coupled code
- 17. Event Aggregator (Pub-Sub) Control Control Control Control Control Control ControlControl A better solution - Loosely coupled code
- 18. 1. Define themessages
- 19. 2. Publish themessages
- 20. 3. Subscribe to-and handle the messages
- 21. NewCustomerControl ToolbarControl Event Aggregator ToolbarControl NewCustomerControl Publish: •DisableSave • EnableSave BtnSave.Enabled = true/false Subscribe to & handle: • DisableSave • EnableSave From strong- to loose coupling
- 22.
- 23. New Requirement The customershould receive an e-mail when the customer has been registered
- 24. 1. Create aNew Class
- 25. 2. Call EmailCustomerFrom RegisterCustomer
- 26. New Requirement Send aSMS to the customer when the customer has been registered
- 27. 1. Create aNew Class
- 28. 2. Call SmsCustomerFrom RegisterCustomer
- 29. Open Closed Principle “Softwareentities (classes, modules, functions, etc.) should be open for extension, but closed for modification” The current implementation breaks this principle Publish-Subscribe would not break the principle RegisterCustomer EmailCustomer SmsCustomer Event Aggregator EmailCustomer SmsCustomer RegisterCustomer Publish message: CustomerRegistered Subscribe to & handle the message Invoke
- 30. 1. Define theMessage
- 31. 2. Create andPublish the Message
- 32. 3. Subscribe tothe Message
- 33. RegisterCustomer EmailCustomer SmsCustomer Event Aggregator EmailCustomerSmsCustomer RegisterCustomer Publish message: CustomerRegistered Subscribe to & handle the message Invoke Overview
- 34. Summary Publish & Subscribe+ Event Aggregator gives: Code that is loosely coupled Less complex code that is easier to maintain and unit-test Where to use it? 1. UI/Presentation layer 2. Other layers when needed How to use it? 1. Download or create your own event aggregator 2. Define a message 3. Create and publish a message 4. Subscribe to the message
- 35.
- 36. The information containedin this presentation is proprietary. © 2012 Capgemini. All rights reserved. www.capgemini.com About Capgemini With more than 120,000 people in 40 countries, Capgemini is one of the world's foremost providers of consulting, technology and outsourcing services. The Group reported 2011 global revenues of EUR 9.7 billion. Together with its clients, Capgemini creates and delivers business and technology solutions that fit their needs and drive the results they want. A deeply multicultural organization, Capgemini has developed its own way of working, the Collaborative Business ExperienceTM, and draws on Rightshore ®, its worldwide delivery model. Rightshore® is a trademark belonging to Capgemini