Elements of the .NET Framework

The .NET Framework consists of three key elements 1 Common Language Runtime 2 .NET Class Library 3 Unifying components

Common Language Runtime The Common Language Runtime (CLR) is a layer between an application and the operating system it executes on. The CLR simplifies an application's design and reduces the amount of code developers need to write because it provides a variety of execution services that include memory management, thread management, component lifetime management, and default error handling. The key benefit of the CLR is that it transparently provides these execution services to all applications, regardless of what programming language they're written in and without any additional effort on the part of the developer. The CLR is also responsible for compiling code just before it executes. Instead of producing a binary representation of your code, as traditional compilers do, .NET compilers produce a representation of your code in a language common to the .NET Framework: Microsoft Intermediate Language (MSIL), often referred to as IL. When your code executes for the first time, the CLR invokes a special compiler called a Just In Time (JIT) compiler, which transforms the IL into executable instructions that are specific to the type and model of your system's processor. Because all .NET languages have the same compiled representation, they all have similar performance characteristics. This means that a program written in Visual Basic .NET can perform as well as the same program written in Visual C++ .NET. (C++ is the language of choice for developers who need the best possible performance a system can deliver.) Common Type System The Common Type System (CTS) is a component of the CLR and provides a common set of data types, each having a common set of behaviors. In Visual Basic, for example, the String data type maps to the CTS System.String class. Therefore, if a JScript .NET client needs to communicate with a component implemented in VB .NET, the client doesn't have to do any additional work to exchange information because it's using a type common to both JScript .NET and VB .NET. The CTS eliminates many interoperability problems that exist outside .NET. .NET programming languages take advantage of the CTS by enabling developers to use their language's built-in data types — the .NET compilers convert the native data types' into their equivalent CTS types at compile time. Developers can also use CTS types directly in their code if they wish. Table 1-2 describes each standard CTS data type. You can use other non-CTS-compliant data types in your applications and components; you're free to use non-CTS-compliant data types, but they may not be available on other implementations of the .NET Framework for other operating systems (see Table 1-3). .NET Class Library In an earlier section, "Consistent programming models across programming languages," the .NET Class Library was described as containing hundreds of classes that model the system and services it provides. To make the .NET Class Library easier to work with and understand, it's divided into namespaces. The root namespace of the .NET Class Library is called System, and it contains core classes and data types, such as Int32, Object, Array, and Console. Secondary namespaces reside within the System namespace. Examples of nested namespaces include the following: § System.Diagnostics: Contains classes for working with the Event Log § System.Data: Makes it easy to work with data from multiple data sources (System.Data.OleDb resides within this namespace and contains the ADO.NET classes) § System.IO: Contains classes for working with files and data streams Figure 1-2 illustrates the relationship between some of the major namespaces in the .NET Class Library. The benefits of using the .NET Class Library include a consistent set of services available to all .NET languages and simplified deployment, because the .NET Class Library is available on all implementations of the .NET Framework. Unifying components Until this point, this chapter has covered the low-level components of the .NET Framework. The unifying components, listed next, are the means by which you can access the services the .NET Framework provides: § ASP.NET § Windows Forms § Visual Studio .NET ASP.NET ASP.NET introduces two major features: Web Forms and Web Services. Web Forms Developers not familiar with Web development can spend a great deal of time, for example, figuring out how to validate the e-mail address on a form. You can validate the information on a form by using a client-side script or a server-side script. Deciding which kind of script to use is complicated by the fact that each approach has its benefits and drawbacks, some of which aren't apparent unless you've done substantial design work. If you validate the form on the client by using client-side JScript code, you need to take into consideration the browser that your users may use to access the form. Not all browsers expose exactly the same representation of the document to programmatic interfaces. If you validate the form on the server, you need to be aware of the load that users might place on the server. The server has to validate the data and send the result back to the client. Web Forms simplify Web development to the point that it becomes as easy as dragging and dropping controls onto a designer (the surface that you use to edit a page) to design interactive Web applications that span from client to server. Web Services A Web service is an application that exposes a programmatic interface through standard access methods. Web Services are designed to be used by other applications and components and are not intended to be useful directly to human end users. Web Services make it easy to build applications that integrate features from remote sources. For example, you can write a Web Service that provides weather information for subscribers of your service instead of having subscribers link to a page or parse through a file they download from your site. Clients can simply call a method on your Web Service as if they are calling a method on a component installed on their system — and have the weather information available in an easy-to-use format that they can integrate into their own applications or Web sites with no trouble. Windows Forms Windows Forms is the name of a unified set of classes that provides support for creating traditional desktop applications — applications that have a graphical user interface (GUI). Windows Forms make it easy to develop end-user applications using any .NET programming language. Furthermore, through Visual Studio .NET, developers can easily design forms by using drag-and-drop editing. Visual Studio .NET Visual Studio .NET fulfills the promise of a single development environment for all languages. Visual Studio .NET simplifies development in a mixed-language environment through features such as support for end-to-end debugging across all programming languages; visual designers for XML, HTML, data, and server-side code; and full IntelliSense support (statement completion). Visual Studio .NET replaces the Visual Basic 6, Visual C++, and Visual InterDev development environments. Visual Studio .NET is able to provide this level of integration because it relies and builds on the facilities of the .NET Framework. Designers for Web forms and Windows Forms enhance developer productivity during the development cycle. Integration of deployment features enhances productivity during post-deployment debugging. Table 1-4 summarizes Visual Studio .NET's major features.