1. A4 Pre

2. Learning Objectives By the end of this assignment, you will:
Re-design a system to make use of the façade design pattern
Use event handling, and the observer design pattern to communicate between modules

3. Learning Objectives By the end of this assignment, you will:
Re-design a system to make use of the façade design pattern
Use event handling, and the observer design pattern to communicate between modules
I think you need to make use of the event handling. But, it’s nothing you haven’t seen. I am pretty sure this assignment cannot be completed without using event handling. However, do not take this as a challenge. ;-)

4. What’s the idea? Redesign the system for extensibility:
New types of products
New forms of payment
New forms of communication
Alternative hardware (this is already done)
Why should we do this?
Future-proofing your system
Think about abstractions and what assumptions you’re making
Someone told you to

5. What it looks like right now
Vending Machine
Coin slot
Selection Buttons
Delivery Chute

6. What it looks like right now
Vending Machine
Coin slot
Selection Buttons
Coin Chutes
Pop Chutes
Delivery Chute

7. What it looks like right now
Vending Machine
Coin slot
Selection Buttons
Delivery Chute

8. What we’d like to do
Vending Machine

9. What we’d like to do 1. Other product types
Vending Machine
”Products” rather
than ”PopCans”

10. What we’d like to do 2. New forms of payment
Vending Machine
Abstract this to allow others to create new ways to pay (e.g. credit card)

11. What we’d like to do 3. New forms of payment
Vending Machine
Abstract this to allow others to interact with the vending machine (e.g. touch screen, voice interaction, etc.)

12. What we’d like to do Abstract these major operations
Vending Machine

13. What we’d like to do Abstract these major operations
Vending Machine

14. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade

15. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade

16. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade …

17. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade

18. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade
Communication Facade

19. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade
Communication Facade …

20. What we’d like to do Abstract these major operations
Vending Machine
Funds or Payment Facade
Communication Facade
Product Facade

21. Funds or Payment Facade
What we’d like to do
Vending Machine
Funds or Payment Facade
Communication Facade
Business Rule
Product Facade

22. Funds or Payment Facade
What we’d like to do
Vending Machine
Funds or Payment Facade
Communication Facade
Business Rule
Product Facade

23. Funds or Payment Facade
What we’d like to do
Funds or Payment Facade
Communication Facade
Business Rule
Product Facade

24. Funds or Payment Facade
What we’d like to do
Business Rule
Funds or Payment Facade
Product Facade
Communication Facade

25. Funds or Payment Facade
What we’d like to do
Business Rule
Funds or Payment Facade
Product Facade
Communication Facade
Notice:
1. Funds, Communication and Product Facades don’t talk to one another.
2. Business Rule is what connects things together – i.e. “when there has been a selection, and there is enough money, then vend the pop, and dispense the change”
3. Notice: business rule does not talk to hardware façade
4. This is a layered architecture
Hardware Facade

26. A few things to keep in mind
Hardware façade communicates upward frequently through events, so the facades need to register for these events
The facades themselves may expose new events (or related events) that other components might be interested in:
e.g. Communication Façade might fire a “SelectionMade” event that might be interesting to both: (1) Business Rule, or (2) a touchscreen display (that communicates only with the communication façade) that shows what was selected
The purpose of this is to enable extensibility, but do not implement (say) a CreditCard module or a TouchScreen module—that is beyond the scope of this assignment
Your goal is to make it such that it would be easy to add such a class into the project, and have it work without having to re-write much

27. Example of Extensibility
CommunicationFacade exists
var lcdScreen = new LCDScreen(communicationFacade);
constructor: registers for SelectionMade event so that it displays what product was selected when it gets selected (i.e. don’t need to modify CommunicationFacade code at all to accommodate for LCDScreen