C# 3.0 Design Patterns

Example: OpenBook

The Bridge pattern gives us a nice opportunity to extend a previous example and to show different patterns interacting. Let's consider the SpaceBook system again. Suppose a developer is working on a new version of SpaceBook called OpenBook. The main feature of OpenBook is that it does not require password authentication. It also does not bother with lazy instantiation, as it is assumed that all OpenBook users will get onto the system straightaway. OpenBook is thus replacing the proxy level of SpaceBook but not the guts of it, and it is certainly the intention that users of both systems should be able to see each other's pages.

QUIZ: Match the Bridge Pattern Players with the .NET Framework Illustration

To test whether you understand the Bridge pattern, cover the lefthand column of the table below and see if you can identify the players among the items from the illustrative examples (Figure 2-6 and Figure 2-7), as shown in the righthand column. Then check your answers against the lefthand column.

Abstraction	NET Framework
Operation	C# compiler
Bridge	Environment Path variable
ImplementationA	3.5 version of the Framework
ImplementationB	2.0.50377 version and build of the Framework
A's OperationImp	3.0 compiler s
B's OperationImp	2.0 compiler

Therefore, we have a design where MyOpenBook and MySpaceBook need to implement a common interface. We shall call this the Bridge interface. The Abstraction is what is commonly called a Portal. It keeps a copy of the appropriate type of book ...