This document discusses design patterns including the provider pattern. It begins by listing some object-oriented programming principles and software architecture patterns. It then focuses on the open-closed principle and how the provider pattern adheres to this principle by allowing new types to be added without modifying existing code. The provider pattern works by dynamically creating instances of classes based on external configuration settings, avoiding the need to modify code. This is compared to the factory pattern, which still requires in-code configuration and modification. Real-world examples of implementing the provider pattern are also provided.

1. Provider Pattern
practices
MINH NGUYEN
@LINKNODE SEPTEMBER, 2015

2. Object-Oriented Programming
23 Design Patterns5 Principles
Single responsibility
Open/closed
Liskov substitution
Integrated segregation
Dependency inversion
Software Architecture
3-tier
MVC
MVP
MVVM
….

3. Open-closed principle
“Software modules should be closed for modifications but open for extensions.”
Sample use case:
Requirements: VentusAR needs to supply a new model type: SolarPanel
Current action: Have to modify all existing code everywhere to support this new type
string message= “”;
if (type = “Wind”)
{
message = “Turbine is spinning”;
}
else if (type = “SolarPanel”)
{
message = “Solar panel is under the sun”;
}
else if ….
else if ….
else if ….
Violate Open-closed principle
(having to modify existing code to be able to add new feature)

4. Inspired by Factory Pattern
VentusModel
+ getMessage()
Turbine
+ getMessage()
SolarPanel
+ getMessage()
Transmission
+ getMessage()
VentusModelFactory
+ getInstant(name)
creates
Client
asks
products

5. Provider Pattern (Microsoft 2002)
* Mimic Plug-in/ Add-on architecture
* Do not have to modify existing code
* Just supply additional separate class
* Configure from external settings (config file, database,)
Create instant from string

6. + External Settings
Provider pattern
From XML:
From Database:
string
string

7. * Supply a new Transmission model to the app without modifying code
Demo

8. Provider Pattern vs Factory Pattern ?
* In-code config
* Still have to modify existing code
* Configure easily from external settings (using .Net Reflection)
* Do not have to modify existing code

9. Q&A