What is required for true cross platform development using .NET? On one hand, not much; on the other hand, a great deal. Because Rotor, Pnet, Mono and (the Microsoft implementation of) .NET, are all based on the ECMA standard, getting a basic C# program running on all four platforms is typically just a matter of copying the .exe file to the machine and executing it (assuming a .NET framework is already on the machine). But what about remoting, serializing and deserializing classes, interoperability, using native code, and non-ECMA classes such as System.Data and System.Windows.Forms (SWF)? This book covers those questions in detail with good practical advice; but that is not the best part of this book. In order to fully understand how cross platform .NET works and does not work, you need to understand the architecture and implementation of the different .NET frameworks; that is where this book really shines. It is full of block diagrams, UML diagrams, and class and code hierarchies. There are some good books on the .NET architecture, but most of these books are too academic and heavy in details for many programmers. This book covers architecture and implantation details from the point of making programs work in different environments, putting it in a nice middle ground; it is an easy to read book, but one that will leave most with a much deeper understanding of .NET interworkings.

The book starts with a brief overview of .NET (including a comparison with Java and the JVM), and a description of how they set up their laboratory for cross-platform testing, then in "Cross-Platform Pitfalls," it covers differences in the intermediate code generated by the three main .NET platforms, Microsoft, Mono, and Pnet. Due to Rotor's license, and its lack of support for anything other than the barest for the .NET framework classes, Rotor is not generally discussed in this book. Chapter 4 looks at the .NET framework classes from the point of what will likely be compatible across the .NET implementations, what will have limitations, and what is just not likely to work. It does this by looking at what operating system calls are made by each namespace in the .NET framework.

In chapter 5 the book looks at making GUI applications cross-platform; this is the area where the most programs are likely to run into cross-platform troubles. This chapter looks at how Microsoft, Mono, and PNET implement System.Drawing and SWF. The book does a good job of describing how Mono implements System.Drawing using gdiplus on windows, and cario on other platforms. This book has been out for a while, so its description of how SWF was implanted using GTK# and WINE are no longer applicable, but is still worth reading for educational purposes. The good news is that SWF is now implemented the same way as System.Drawing, so simply applying that section to SWF brings the book up to date on this issue. This chapter also covers several GUI toolkits (SWF, GTK#, QT#, TickleSharp, #WT, wx.NET) that can be used to build cross-platform applications, compares their capabilities, and finally shows a way to write GUI toolkit independent code using the Model-View-Controller (MVC) pattern. When reading this chapter, one also needs to consider that when this book was written, the implementation of SWF was just starting; it is now nearing completion.

Chapter 6 starts to cover distributed applications by showing how to access the different backend databases available. It goes on to create an application that can run under application servers such as IIS, Mono's own XSP server, or as a mod_mono module under Apache, and closes with a overview of Web services.

Chapter 7 covers the ins and outs of calling native code on different OSs including security, path resolution, marshaling, calling conventions, and invoking C++ code from .NET using the Simplified Wrapper and interface Generator tool, SWIG.

Chapter 8 opens with a discussion of interoperability between 24 different .NET languages, including how to run Java programs under .NET using IKVM, an open source Java Virtual Machine written in .NET that runs under both the Mono and Microsoft runtimes. It then covers the remoting architecture and channels including a cross-platform logging application. It finishes with a long section on interoperating with CORBA and cross-platform COM.

The book closes with cross-platform building using NAnt, and cross-platform testing using NUnit; it also looks at the future (some of which is now) including .NET 2.0, VS2005, and Longhorn, and tries to peer into the future of Mono and PNet.

This book is one of my favorites, and I think every .NET developer should have a copy of this book, even if they are not interested in cross platform development. Its approachable discussion of what .NET is, and how it works, is unique in all the .NET books I have read.

SIDEBAR

Title: Cross-Platform .NET Development
Author: M.J. Easton and Jason King
Publisher: Apress
ISBN #: 1-59059-330-8
Price: US $49.99