Programming .NET Components

Gianluca Insolvibile writes "I plead guilty: I have always admired Microsoft's COM architecture and the relative simplicity that allows you to reuse already installed components to create even complex programs. And I have always been fascinated by the distributed nature of DCOM, which seemed to me much more graspable than complex monsters like CORBA and J2EE. While looking for equally expressive Open Source component technologies among GNOME and KDE, I was never able to find something fitting my needs (I never got into Bonobo deeply enough, though)." Read on to see how this led Gianluca to Juval Loewy's O'Reilly-published Programming .NET Components, and what he thinks of the book. Programming .NET Components author Juval Loewy pages 460 publisher O'Reilly rating 7.5 reviewer Gianluca Insolvibile ISBN 0596003471 summary An introduction to components-oriented development with the tools and services provided by the .NET framework

One day, I stumbled upon the mono and Portable.NET projects, which are trying to bring all the .NET stuff to the penguin platform. This was the main reason that convinced me to learn more on .NET: open specs, a component-enabling technology, the cross-platform mirage, a completely new (well, sort of) set of concepts to be grasped, and something which I could use both on Linux and on Windows.

Armed with these expectations, I decided to look for a good introductory text on the .NET framework focused on components development. Among the plethora of publications on the subject, I decided to stick with a publisher having a long and respectable tradition in Open Source related books. Among the herd of funny beasts that populate O'Reilly's catalog, I picked out a "land hermit crab," aka Programming .NET Components, by Juval Loewy.

Overview The book begins with a chapter giving a rationale behind component-oriented programming versus object-oriented programming, that is, interfaces versus inheritance. The second chapter shows how those concepts are reflected in the .NET Framework, briefly introducing the Common Language Runtime (CLR), the Intermediate Language (IL) and .NET Assemblies. The following three chapters deal with interface-based programming, objects lifecycle management and versioning, gradually introducing the underlying concepts and showing how they become concrete in the .NET framework (more specifically, by using the C# language). No formal introduction to C# language constructs is given, but if you are familiar with C++ or Java you will be able to follow the code snippets fairly easily.

Events and asynchronous code execution are the subjects of Chapters 6 and 7, respectively. While the former is just a quick introduction to the C# approach to delegates and events (yet useful if you are new to the matter), the chapter on asynchronous calls is much more substantial. The mechanics behind async calls are explained, together with pros and cons of using callbacks, BeginInvoke() and EndInvoke() calls, one-way methods, and so on.

Chapter 8 is devoted to Multithreading and Concurrency. Commonplace concepts like threads application and usage are explained, as always dressed with a bit of C# syntax. While such concepts are easily found in any multithreaded programming tutorial on the Internet, explaining them from the basics never hurts -- and prepares the reader to the most insidious traps of multithreaded programming. Synchronization appropriately takes a fair part of Chapter 8: automatic and manual synchronization provided by the .NET runtime environment are explained, together with the concepts of contexts and synchronization domains. This part is quite interesting, since it delves into .NET specific concepts which are quite new to programmers who had a happy Microsoft-less childhood (though they might not be so new to people who speak COM fluently). Other .NET threading related services (such as timers) are presented at the end of the chapter.

Chapter 9, devoted to object serialization and persistence, describes how live objects can be transformed (formatted) into a stream of bytes to be sent over a network channel, or stored on a persistent storage medium. This chapter lays the grounds for the exacting chapter on remoting, which follows immediately. Chapter 10 is the longest and most content-rich chapter of the book: first, the entire story of native processes, .NET app domains and assemblies is told. After reading it here, it won't look so confusing as before. Then, objects marshaling, remote callbacks, synchronization and activation modes are described, including client and server activated, single-call and singleton modes. Afterwards, the author gets to a global overview of the .NET remoting architecture, its basic building blocks (like proxies, transport channels and call dispatchers) and working mechanisms (like type registration and environment configuration). A reprise on objects sponsorship and leasing closes the chapter and completes the discussion on objects' lifecycle left pending in Chapter 4. Chapter 10 offers a lot of interesting cues, but unfortunately cannot dig deeply enough in the subject (after all, this is not a book on remoting). Many people (including Juval himself) recommend Ingo Rammer's Advanced .NET Remoting (APress) to learn more on the topic, but I have yet to get my hands on it.

Chapter 11 reprises the description of contexts in .NET, this time focusing on calls interception. The whole interception architecture is described with a fair level of detail and, as always, in a clear and understandable way. Context-agile and context-bound objects are described, as well as .NET and custom component services. While reading this chapter, you start understanding that contexts, app domains, call interception and remoting are tightly interwoven and that their full understanding is the real key to the exploitation of the .NET platform potential. Unfortunately, this is where the book leaves you alone -- but I strongly suspect that a full coverage of these topics would have required an entire book on its own.

The last chapter of the book deals with the .NET Security architecture, introducing the concepts of permissions, code groups and policies. Security administration is explained, both from a system configuration and a programmatic point of view.

What's to like What I liked most is the straightforward approach of the author in introducing the rationale behind components, components-based programming and their support in the .NET Framework: each concept is walked through step-by-step, instead of being presented in a complete working example with little or no explanation. Hence, you won't get working code on page 3 of the book -- instead, you will gradually learn how to write some.

Indeed, I found the description of awkward concepts like asynchronous calls, multithreading and remoting very clear, even for someone with no previous experience with .NET and C#.

I also consider a plus the broad experience the author has in the field, which shines through the many programming hints given, and in lots of references to concepts in COM which have an homologous in .NET.

I finally found the book to have the right balance between printed code and text (that is: do not fill hundreds of pages with code, I'll look at it online).

What's to consider Programming .NET Components is just an introductory book: it points you in the right direction toward components programming with .NET, but does not bring you very far. If you are really serious about learning .NET advanced topics, you will need a more specific tome to complement (or substitute for) this one.

More specifically, the 70 pages which cover remoting are just an introduction to the matter. The same applies to some of the most important concepts revolving around .NET (app domains, contexts, and the like).

Finally, despite the subtitle ("Design and Build Maintainable Systems using Components-Oriented Programming"), be warned that this is not at all a book on software design (components oriented programming is covered in just 15 pages).

The summary Reading the book goes without a glitch, thanks to a smooth writing style and a very structured approach to explaining concepts. Still, when I turned the last page of the book I felt that my understanding of components within the .NET platform was far from complete.

.NET Components Programming is quite fair to its title: it will teach you how to program components by using .NET constructs, but (apart from some quick notes here and there) it will not provide extensive coverage of components oriented design and development. If you are already familiar with .NET concepts and are looking for something shedding light on components programming, this book will not help you significantly. On the contrary, if you know something about components and want to start developing them into the .NET Framework, this will surely be an interesting read.

Table of Contents
Preface
Chapter 1. Introducing Component-oriented programming
Chapter 2. .NET Component-oriented Programming Essentials
Chapter 3. Interface-based Programming
Chapter 4. Lifecycle Management
Chapter 5. Version Control
Chapter 6. Events
Chapter 7. Asynchronous Calls
Chapter 8. Multithreading and Concurrency Management
Chapter 9. Serialization and Persistence
Chapter 10. Remoting
Chapter 11. Context and Interception
Chapter 12. Security
Appendix A. Interface-based Web-services
Appendix B. Custom Security Principal
Appendix C. Reflection and Attributes

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Comments

DCOM vs .NET?

[chochos]

So you admire DCOM and that's why you recomment a book about .NET which brings a new way of doing things to get away from the mess that is DCOM? now it looks a lot more like J2EE...