Chapter 9. Building an Application Block

THE PREVIOUS CHAPTERS have described the design for each of the application blocks that ship with Enterprise Library, how to configure them, and how to develop an application so that it can benefit from the application blocks. They have emphasized how the design of each block is not only an implementation of the best practices as promoted by the Microsoft patterns & practices team, but that special attention was paid to ensure the block was simple to use and extensible to fit the needs of many enterprises.

You saw how each application block can be extended so that you can mold them to fit your needs if your application requirements don't perfectly match the providers that ship with Enterprise Library. For example, Chapter 6 showed how the Logging and Instrumentation Application Block can be extended with a new distribution strategy and Distributor Service for enterprises that may not have standardized or do not promote the use of MSMQ.

The extensibility of Enterprise Library does not end with the ability to extend each application block. If you have a particular need that is not addressed by any of the application blocks that ship with Enterprise Library, you can develop a new application block that has the same design-time and configuration-driven capabilities as the application blocks that ship with Enterprise Library. This chapter walks you through the steps that are needed to create a new application block that can serve as a peer to the application blocks that ship with Enterprise Library.

To fully appreciate this chapter, I highly recommend that you first read Chapters 1 and 2. Understanding the contents of those chapters is important because all application blocks, including the one that is created in this chapter, depend on the Configuration Application Block for reading and writing its configuration information and enabling its design-time features. While this chapter recaps some of the important points detailed in those two chapters, it doesn't go into the depth that those chapters do.

Additionally, I recommend having read Chapters 3 and 4. While these aren't required reading to understand the concepts for how to build an application block, the block that I create in this chapter makes extensive use of the Data Access Application Block and the Caching Application Block by encapsulating and extending their functionality. Therefore, understanding those application blocks will help you understand the application block created in this chapter.