Exploring the Observer Design Pattern

Summary: This article discusses the use of design patterns in the Microsoft .NET Framework. An extremely powerful tool for developers or architects in development projects, design patterns ensure that common problems are addressed via well-known and accepted solutions, and that correct code is developed more rapidly, reducing the chance that a mistake will occur in design or implementation. (21 printed pages)

Introduction
Why Design Patterns?
.NET Framework Patterns
   Observer Pattern
   Event Pattern
Conclusion

Introduction

During the course of a given development project, it is not uncommon to use the concept of design patterns to address certain problems relating to application design and architecture. However, the definition of design patterns is often difficult to convey with any level of accuracy; as such, the concept warrants a brief examination of origin and history.

The origin of software design patterns is attributed to the work of Christopher Alexander. As a building architect, Alexander noted the presence of common problems and related solutions within a given context. A design pattern, as Alexander termed this problem/solution/context triad, enabled an architect to rapidly address issues in a uniform manner during building design. First published twenty-five years ago, A Pattern Language: Towns, Buildings, Construction (Alexander et al, Oxford University Press, 1977) introduced over 250 architectural design patterns and provided the basis for the inclusion of this concept into the realm of software development.

In 1995, the software industry was first widely introduced to the design patterns as they directly related to building applications. The four authors, Gamma, Helm, Johnson, and Vlissides (collectively known as the Gang of Four, or GoF), intersected Alexander's design patterns with the burgeoning object-oriented software movement in their work, Design Patterns: Elements of Reusable Object-Oriented Software (Addison-Wesley Pub Co, 1995). Based on their collective experience and examination of existing object frameworks, the GoF provided 23 design patterns that examined common problems and solutions encountered while designing and architecting applications. Following that publication, the concept of design patterns has grown to encompass many problems and solutions encountered in the software domain. In fact, the popularity of design patterns has given rise to the concept of anti-patterns, which are solutions that commonly worsen, rather than solve, the problem at hand.

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