By Andrew Troelsen
The funny thing about writing a book on COM and .NET interoperability is that one author could craft a five- to ten-page article describing the basic details that you must understand to get up and running with interop-related endeavors. At the same time, another author could write volumes of material on the exact same subject. So, you may be asking, how could this massive discrepancy between authors possibly exist?
Well, stop and think for a moment about the number of COM-aware programming languages and COM application frameworks that exist. Raw C++/IDL, ATL, MFC, VB 6.0, and Object Pascal (Delphi) each have their own syntactic tokens that hide the underbelly of COM from view in various ways. Thus, the first dilemma you face as an interop author is choosing which language to use to build the COM sample applications.
Next, ponder the number of .NET-aware programming languages that are either currently supported or under development. C#, VB .NET, COBOL .NET, APL .NET, PASCAL .NET, and so on, each have their own unique ways of exposing features of the CTS to the software engineer. Therefore, the next dilemma is choosing which language to use to build the .NET applications.
Even when you solve the first two dilemmas and choose the languages to use during the course of the book, the final dilemma has to do with the assumptions made regarding the readers themselves. Do they have a solid understanding of IDL and the COM type system? Do they have a solid understanding of the .NET platform, managed languages, and metadata? If not, how much time should be spend pounding out such details?
Given the insane combinations of language preferences and reader backgrounds, I have chosen to take a solid stance in the middle ground. If I have done my job correctly, you will walk away from this text with the skills you need to tackle any interop-centric challenge you may encounter. Also, I am almost certain you will learn various tantalizing tidbits regarding the COM and .NET type systems.
My ultimate goal in writing this book is to provide you with a solid foundation of COM and .NET interoperability. To achieve this goal, I have chosen to provide material that defines the finer details of the COM and .NET architectures. For example, over the course of the first six chapters, you will learn how to programmatically generate and parse COM IDL, dynamically generate C# and VB .NET source code on the fly (via System.CodeDOM), and build .NET applications that can read COM type information. After all, when you need to build a software solution that makes use of two entirely unique programming paradigms, you had better have a solid understanding of each entity.
However, once this basic foundation has been laid, the bulk of this book describes the process of making COM and .NET binaries coexist in harmony. As an added bonus, I cover the process of building .NET code libraries that can leverage the services provided by the COM+ runtime layer (via System.EnterpriseServices).