Introduction

If we were to describe the C# language and its associated environment, the .NET Framework, as the most important new technology for developers for many years, we would not be exaggerating. .NET is designed to provide a new environment within which you can develop almost any application to run on Windows, while C# is a new programming language that has been designed specifically to work with.NET. Using C# you can, for example, write a dynamic Web page, an XML Web service, a component of a distributed application, a database access component, a classic Windows desktop application, or even a new smart client application that allows for online/offline capabilities. This book covers the .NET Framework 2.0, the third release of the framework. If you are coding using version 1.0 or 1.1, there may be sections of the book that will not work for you. We try to notify you of items that are new to the .NET Framework 2.0 specifically.

Don't be fooled by the .NET label. The NET bit in the name is there to emphasize Microsoft's belief that distributed applications, in which the processing is distributed between client and server, are the way forward, but C# is not just a language for writing Internet or network-aware applications. It provides a means for you to code up almost any type of software or component that you might need to write for the Windows platform. Between them, C# and .NET are set both to revolutionize the way that you write programs, and to make programming on Windows much easier than it has ever been.

That's quite a substantial claim, and it needs to be justified. After all, we all know how quickly computer technology changes. Every year Microsoft brings out new software, programming tools, or versions of Windows, with the claim that these will be hugely beneficial to developers. So what's different about.NET and C#?

The Significance Of .NET And C#

In order to understand the significance of .NET, it is useful to remind ourselves of the nature of many of the Windows technologies that have appeared in the past ten years or so. Although they may look quite different on the surface, all of the Windows operating systems from Windows 3.1 (introduced in 1992) through Windows Server 2003 have the same familiar Windows API at their core. As we've progressed through new versions of Windows, huge numbers of new functions have been added to the API, but this has been a process of evolving and extending the API rather than replacing it.

The same can be said for many of the technologies and frameworks that we've used to develop software for Windows. For example, COM (Component Object Model) originated as OLE (Object Linking and Embedding). At the time, it was, to a large extent, simply a means by which different types of Office documents could be linked, so that, for example, you could place a small Excel spreadsheet in your Word document. From that it evolved into COM, DCOM (Distributed COM), and eventually COM+ — a sophisticated technology that formed the basis of the way almost all components communicated, as well as implementing transactions, messaging services, and object pooling.

Microsoft chose this evolutionary approach to software for the obvious reason that it is concerned about backward compatibility. Over the years a huge base of third-party software has been written for Windows, and Windows wouldn't have enjoyed the success it has had if every time Microsoft introduced a new technology it broke the existing code base!

While backward compatibility has been a crucial feature of Windows technologies and one of the strengths of the Windows platform, it does have a big disadvantage. Every time some technology evolves and adds new features, it ends up a bit more complicated than it was before.

It was clear that something had to change. Microsoft couldn't go on forever extending the same development tools and languages, always making them more and more complex in order to satisfy the conflicting demands of keeping up with the newest hardware and maintaining backward compatibility with what was around when Windows first became popular in the early 1990s. There comes a point where you have to start with a clean slate if you want a simple yet sophisticated set of languages, environments, and developer tools, which makes it easy for developers to write state-of-the-art software.

This fresh start is what C# and .NET are all about. Roughly speaking, .NET is a framework—an API— for programming on the Windows platform. Along with the .NET Framework, C# is a language that has been designed from scratch to work with .NET, as well as to take advantage of all the progress in developer environments and in our understanding of object-oriented programming principles that have taken place over the past 20 years.

Before we continue, we should make it clear that backward compatibility has not been lost in the process. Existing programs will continue to work, and .NET was designed with the ability to work with existing software. Presently, communication between software components on Windows almost entirely takes place using COM. Taking account of this, .NET does have the ability to provide wrappers around existing COM components so that .NET components can talk to them.

It is true that you don't need to learn C# in order to write code for .NET. Microsoft has extended C++, provided another new language called J#, and made substantial changes to Visual Basic to turn it into the more powerful language Visual Basic .NET, in order to allow code written in either of these languages to target the .NET environment. These other languages, however, are hampered by the legacy of having evolved over the years rather than having been written from the start with today's technology in mind.

This book will equip you to program in C#, while at the same time provide the necessary background in how the .NET architecture works. We will not only cover the fundamentals of the C# language but also go on to give examples of applications that use a variety of related technologies, including database access, dynamic Web pages, advanced graphics, and directory access. The only requirement is that you be familiar with at least one other high-level language used on Windows — either C++, Visual Basic, or J++.

Advantages of .NET

We've talked in general terms about how great .NET is, but we haven't said much about how it helps to make your life as a developer easier. In this section, we'll discuss some of the improved features of .NET in brief.

• Object-Oriented Programming — both the .NET Framework and C# are entirely based on object-oriented principles right from the start.

• Good Design — a base class library, which is designed from the ground up in a highly intuitive way.

• Language Independence — with .NET, all of the languages Visual Basic .NET, C#, J#, and managed C++ compile to a common Intermediate Language. This means that languages are inter- operable in a way that has not been seen before.

• Better Support for Dynamic Web Pages — while ASP offered a lot of flexibility, it was also inefficient because of its use of interpreted scripting languages, and the lack of object-oriented design often resulted in messy ASP code. .NET offers an integrated support for Web pages, using a new technology — ASP.NET. With ASP.NET, code in your pages is compiled, and may be written in a .NET-aware high-level language such as C#, J#, or Visual Basic 2005.

• Efficient Data Access — a set of .NET components, collectively known as ADO.NET, provides efficient access to relational databases and a variety of data sources. Components are also available to allow access to the file system, and to directories. In particular, XML support is built into .NET, allowing you to manipulate data, which may be imported from or exported to non-Windows platforms.

• Code Sharing — .NET has completely revamped the way that code is shared between applications, introducing the concept of the assembly, which replaces the traditional DLL. Assemblies have formal facilities for versioning, and different versions of assemblies can exist side by side.

• Improved Security — each assembly can also contain built-in security information that can indicate precisely who or what category of user or process is allowed to call which methods on which classes. This gives you a very fine degree of control over how the assemblies that you deploy can be used.

• Zero Impact Installation — there are two types of assembly: shared and private. Shared assemblies are common libraries available to all software, while private assemblies are intended only for use with particular software. A private assembly is entirely self-contained, so the process of installing it is simple. There are no registry entries; the appropriate files are simply placed in the appropriate folder in the file system.

• Support for Web Services — .NET has fully integrated support for developing Web services as easily as you'd develop any other type of application.

• Visual Studio 2005 — .NET comes with a developer environment, Visual Studio 2005, which can cope equally well with C++, C#, J#, and Visual Basic 2005, as well as with ASP.NET code. Visual Studio 2005 integrates all the best features of the respective language-specific environments of Visual Studio .NET 2002/2003 and Visual Studio 6.

• C# — C# is a new object-oriented language intended for use with .NET.

We will be looking more closely at the benefits of the .NET architecture in Chapter 1.