Like most of the design patterns we’ve dealt with both in our book and on this blog we like to start with a minimalist example and then provide a more concrete and useful example. With the Bridge design pattern, the example is fairly minimalist, but it has been designed to create graphic backdrops for video objects. So, while not exactly minimalist and certainly not abstract, the Bridge example here is still fairly simple. (Well, at least as simple as design patterns ever get.) Besides, it accomplished something I needed.
Bridge Over Untroubled Waters
With most design patterns I’ve found that their abstract concepts are clearer than their actual creation. (The Mediator design pattern in this blog is a good example.) However, with the Bridge, I found that the concept was a bit muddled, but making a Bridge design pattern that actually accomplished something useful was relatively simple. To get started, take a look at the class diagram in Figure 1:
Figure 1: Bridge Class Diagram
The intent of the Bridge pattern is to decouple an abstraction from its implementation so that the two can vary independently. (GoG 151) If you don’t think about that much, it sounds like a good idea to keep an application from grinding its gears when a change is made in either the abstraction or implementation. The Freemans (Head First Design Patterns, pp. 612-613) have a great example—a universal remote control. The remote control is the abstraction and a TV set is the implementor. Concrete implementors are the different brands of TVs. As new technology arises, the remote control can be updated with new gizmos. Likewise, the TV sets can also be updated and different brands will have their own unique features. A good Bridge design will allow each to be changed without breaking the other. So far so good.
Continue reading ‘An ActionScript Bridge Design Pattern: Flexibility Making Backdrops’
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