Design patterns capture best user practices and describe the possible solutions to a problem in context; depicting generic example of real life scenarios. Last night in LA . NET developers’ group meeting, David Wells, President OCIUG and OCNSUG spoke about software design patterns and their implementation in development frameworks. This event about software reusability techniques was held in UCLA Dodd’s hall with Scott Robertson, President LA .NET Developers group’s opening keynote and usual announcements. Jeffrey Hasan announced he’ll be delivering next months’ presentation on “Build Message-Based Web Services for Service Oriented Applications” on 3^rd May 2004. 

David’s speech was a breadth first approach to Design patterns; He began with examples from classical texts; Addison-Wesley’s Design Patterns which is considered a-must-read for Software design Engineers. This book is commonly known as GOF (Gang of four) after authors Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides. A detailed overview of GOF Patterns and there frequency of usage in projects can be found here. David’s listed patterns in the following unclassified order.

 One can always disagree with this list and there could various additions for instance I miss “Agile development” and aspect oriented programming.  

Software patterns, as he defined them, are classified into three major categories; Behavioral, Creational and Structural patterns. He later elaborated each of the types as follows.

David’s presentation can be downloaded from OCIUG website as he promised to upload the latest version soon; Observer and  Singleton Presentation & code samples are already uploaded. For Singleton Design Pattern, Exploring the Singleton Design Pattern by Mark Townsend of Microsoft Corporation is a good reading. (David Wells used the illustration in this article during the presentation). Observer is implemented in both major development frameworks in the form of delegates and call back features; System.IO.FileSystemWatcher is a good example of Observer Pattern. It is mostly low-level implementation (multithreaded event handler attachment), and appears in its entirety as part of other important patterns (e.g. ModelViewController).

Couple of things which he emphasized on during the talk, and I remembered, other than classical Singleton and Factory patterns were Refactoring and XP. Refactoring is code oriented optimization approach defined as “is a disciplined technique for restructuring an existing body of code, altering its internal structure without changing its external behavior.” In simple words its better & optimized code. There is a collection of tools available for different IDE’s and platforms on Martin Fowler’s Refactoring.com; (also includes my favorite C# refactory listed). Refactoring in Whidbey by Scott Water, Refactoring in VS.NET Whidbey hands on labs PDC  Visual C# "Whidbey": IDE Enhancements For C# Devlopers  are good articles to read for those interested in up coming IDE’s support for Refactoring.

Extreme Programming is the approach to create better, deliberate and disciplined software projects; most suitable for dynamic and altering requirement projects (Iterative Model of Software Engineering), XP revolves around planning, coding, designing and testing phases which are defined here in greater detail as XP rules.

Later during discussion data access patterns, business object patterns, use case patterns, . NET patterns, CRC (Class, Responsibilities, and Collaborators) cards were being explained. Anti Patterns are bad approaches combined together for developers to beware of potential development pitfalls; David stated what’s mentioned on Anti-Patterns Home “A survey of hundreds of corporate software development projects indicated that five out of six software projects are considered unsuccessful. About a third of software projects are canceled. The remaining projects delivered software that was typically twice the expected budget and took twice as long to developed as originally planned [Johnson 95].” Some of the anti-patterns are Blob, Lava flow, Spaghetti code etc.

I found another good definition of Anti-Patterns here. “An AntiPattern is a pattern that tells how to go from a problem to a bad solution. (Contrast to an AmeliorationPattern, which is a pattern that tells how to go from a bad solution to a good solution.)”

The presentation ended with a raffle and I won a cool LA . NET developers group coffee mug :D

Recommended Readings

• Refactoring: Improving the Design of Existing Code
  by Martin Fowler, Kent Beck , John Brant , William Opdyke , Don Roberts
• Implementing the Singleton Pattern in C#
•  Implementing Singleton in C# (MSDN)
• Microsoft Patterns & Practices
• Complete list of patterns & practices
• Abstract Factory Patterns in C#
• Exploring the Factory Design Pattern
• Enterprise Solution Patterns Using Microsoft .NET
• Lifecycle Practices 
•  Anti Patterns Catalog
•  Anti-Patterns and Patterns in Software Configuration Management
  by William J. Brown, Hays W. McCormick, Scott W. Thomas