The seven pillars of aspnet

The Seven Pillars of ASP.NET
When ASP.NET was first released, there were seven key facts that differentiated it from previous
Microsoft products and competing platforms. If you’re coming to ASP.NET from another web
development platform, or you’re an old-hand .NET coder who has yet to try programming for the Web,
these sections will quickly give you a bit of ASP.NET insight.

#1: ASP.NET is integrated with the .NET Framework
The .NET Framework is divided into an almost painstaking collection of functional parts, with tens of
thousands of types (the .NET term for classes, structures, interfaces, and other core programming
ingredients). Before you can program any sort of .NET application, you need a basic understanding of
those parts—and an understanding of why things are organized the way they are. The massive collection
of functionality that the .NET Framework provides is organized in a way that traditional Windows
programmers will see as a happy improvement. Each one of the thousands of classes in the .NET
Framework is grouped into a logical, hierarchical container called a namespace. Different namespaces
provide different features. Taken together, the .NET namespaces offer functionality for nearly every
aspect of distributed development from message queuing to security. This massive toolkit is called the
class library.

Interestingly, the way you use the .NET Framework classes in ASP.NET is the same as the way you use
them in any other type of .NET application (including a stand-alone Windows application, a Windows
service, a command-line utility, and so on). Although there are Windows-specific and web-specific
classes for building user interfaces, the vast majority of the .NET Framework (including everything from
database access to multithreaded programming) is usable in any type of application. In other words,
.NET gives the same tools to web developers that it gives to rich client developers.

■ Tip: One of the best resources for learning about new corners of the .NET Framework is the .NET
Framework class library reference, which is part of the MSDN Help library reference. If you have Visual
Studio 2008 installed, you can view the MSDN Help library by clicking the Start button and choosing
Programs ➤ Microsoft Visual Studio 2010 ➤ Microsoft Visual Studio 2010 Documentation (the exact
shortcut depends on your version of Visual Studio). Or, you can find the most recent version of the class
library reference online at

http://tinyurl.com/2d42w5e.

#2: ASP.NET Is Compiled, Not Interpreted

ASP.NET applications, like all .NET applications, are always compiled. In fact, it’s impossible to execute
C# or Visual Basic code without it being compiled first.

.NET applications actually go through two stages of compilation. In the first stage, the C# code you write
is compiled into an intermediate language called Microsoft Intermediate Language (MSIL), or just IL. This
first step is the fundamental reason that .NET can be language-interdependent. Essentially, all .NET
languages (including C#, Visual Basic, and many more) are compiled into virtually identical IL code. This
first compilation step may happen automatically when the page is first requested, or you can perform it
in advance (a process known as pre-compiling). The compiled file with IL code is an assembly.

The second level of compilation happens just before the page is actually executed. At this point, the IL
code is compiled into low-level native machine code. This stage is known as just-in-time (JIT)
compilation, and it takes place in the same way for all .NET applications (including Windows
applications, for example). Figure 1-1 shows this two-step compilation process.

.NET compilation is decoupled into two steps in order to offer developers the most convenience and the
best portability. Before a compiler can create low-level machine code, it needs to know what type of
operating system and hardware platform the application will run on (for example, 32-bit or 64-bit
Windows). By having two compile stages, you can create a compiled assembly with .NET code and still
distribute this to more than one platform.

Of course, JIT compilation probably wouldn’t be that useful if it needed to be performed every time a
user requested a web page from your site. Fortunately, ASP.NET applications don’t need to be compiled
every time a web page is requested. Instead, the IL code is created once and regenerated only when the

source is modified. Similarly, the native machine code files are cached in a system directory that has a
path like c:WindowsMicrosoft.NETFramework[Version]Temporary ASP.NET Files.

The actual point where your code is compiled to IL depends on how you’re creating and deploying your
web application. If you’re building a web project in Visual Studio, the code is compiled to IL when you
compile your project. But if you’re building a lighter-weight project less website, the code for each page
is compiled the first time you request that page. Either way, the code goes through its second
compilation step (from IL to machine code) the first time it’s executed.

ASP.NET also includes pre-compilation tools that you can use to compile your application right down to
machine code once you’ve deployed it to the production web server. This allows you to avoid the
overhead of first-time compilation when you deploy a finished application (and prevent other people
from tampering with your code).

#3: ASP.NET Is Multilanguage

Though you’ll probably opt to use one language over another when you develop an application, that
choice won’t determine what you can accomplish with your web applications. That’s because no matter
what language you use, the code is compiled into IL.

IL is a stepping stone for every managed application. (A managed application is any application that’s
written for .NET and executes inside the managed environment of the CLR.) In a sense, IL is the language
of .NET, and it’s the only language that the CLR recognizes.

To understand IL, it helps to consider a simple example. Take a look at this code written in C#:

using System;
namespace HelloWorld
{
public class TestClass
{
static void Main(string[] args)
{
Console.WriteLine("Hello World");
}
}
}
This code shows the most basic application that’s possible in .NET—a simple command-line utility that
displays a single, predictable message on the console window. Now look at it from a different
perspective. Here’s the IL code for the Main() method:

.method private hidebysig static void Main(string[] args) cil managed
{
.entrypoint
// Code size 13 (0xd)
.maxstack 8
IL_0000: nop

IL_0001: ldstr "Hello World"
IL_0006: call void [mscorlib]System.Console::WriteLine(string)
IL_000b: nop
IL_000c: ret
} // end of method TestClass::Main

It’s easy enough to look at the IL for any compiled .NET application. You simply need to run the IL
Disassembler, which is installed with Visual Studio and the .NET SDK (software development kit). Look
for the file ildasm.exe in a directory like c:Program FilesMicrosoft SDKsWindowsv7.0Abin. Run
ildasm.exe, and then use the File ➤ Open command, and select any DLL or EXE that was created with
.NET.

■ Tip: For even more disassembling power, check out the remarkable (and free) Reflector tool at
http://www.red-gate.com/products/reflector. With the help of community-created add-ins, you can use
Reflector to diagram, analyze, and decompile the IL code in any assembly.

If you’re patient and a little logical, you can deconstruct the IL code fairly easily and figure out what’s
happening. The fact that IL is so easy to disassemble can raise privacy and code control issues, but these
issues usually aren’t of any concern to ASP.NET developers. That’s because all ASP.NET code is stored
and executed on the server. Because the client never receives the compiled code file, the client has no
opportunity to decompile it. If it is a concern, consider using an obfuscator that scrambles code to try to
make it more difficult to understand. (For example, an obfuscator might rename all variables to have
generic, meaningless names such as f__a__234.) Visual Studio includes a scaled-down version of one
popular obfuscator, called Dotfuscator.

The following code shows the same console application in Visual Basic code:

Imports System
Namespace HelloWorld
Public Class TestClass
Shared Sub Main(args() As String)
Console.WriteLine("Hello World")
End Sub
End Class
End Namespace

If you compile this application and look at the IL code, you’ll find that it’s nearly identical to the IL code
generated from the C# version. Although different compilers can sometimes introduce their own
optimizations, as a general rule of thumb no .NET language outperforms any other .NET language,
because they all share the same common infrastructure. This infrastructure is formalized in the CLS
(Common Language Specification), which is described in the following sidebar, entitled “The Common
Language Specification.

” It’s worth noting that IL has been adopted as an Ecma and ISO standard. This adoption allows the
adoption of other common language frameworks on other platforms. The Mono project at
http://www.mono-project.com is the best example of such a project.

The Common Language Specification

The Common Language Specification
The CLR expects all objects to adhere to a specific set of rules so that they can interact. The CLS is this set
of rules.

The CLS defines many laws that all languages must follow, such as primitive types, method overloading,
and so on. Any compiler that generates IL code to be executed in the CLR must adhere to all rules
governed within the CLS. The CLS gives developers, vendors, and software manufacturers the opportunity
to work within a common set of specifications for languages, compilers, and data types. You can find a
list of a large number of CLS-compliant languages at http://dotnetpowered.com/languages.aspx.

Given these criteria, the creation of a language compiler that generates true CLR-compliant code can be
complex. Nevertheless, compilers can exist for virtually any language, and chances are that there may
eventually be one for just about every language you’d ever want to use. Imagine—mainframe
programmers who loved COBOL in its heyday can now use their knowledge base to create web
applications!

#4: ASP.NET Is Hosted by the Common Language Runtime

Perhaps the most important aspect of the ASP.NET engine is that it runs inside the runtime environment
of the CLR. The whole of the .NET Framework—that is, all namespaces, applications, and classes—is
referred to as managed code. Though a full-blown investigation of the CLR is beyond the scope of this
chapter, some of the benefits are as follows:

Automatic memory management and garbage collection: Every time your application instantiates a
reference-type object, the CLR allocates space on the managed heap for that object. However, you
never need to clear this memory manually. As soon as your reference to an object goes out of scope (or
your application ends), the object becomes available for garbage collection. The garbage collector runs
periodically inside the CLR, automatically reclaiming unused memory for inaccessible objects. This model
saves you from the low-level complexities of C++ memory handling and from the quirkiness of COM
reference counting.
Type safety: When you compile an application, .NET adds information to your assembly that indicates
details such as the available classes, their members, their data types, and so on. As a result, other
applications can use them without requiring additional support files, and the compiler can verify that
every call is valid at runtime. This extra layer of safety completely obliterates whole categories of low-
level errors.
Extensible metadata: The information about classes and members is only one of the types of metadata
that .NET stores in a compiled assembly. Metadata describes your code and allows you to provide
additional information to the runtime or other services. For example, this metadata might tell a
debugger how to trace your code, or it might tell Visual Studio how to display a custom control at design
time. You could also use metadata to enable other runtime services, such as transactions or object
pooling.
Structured error handling: .NET languages offer structured exception handling, which allows you to
organize your error-handling code logically and concisely. You can create separate blocks to deal with
different types of errors. You can also nest exception handlers multiple layers deep.
Multithreading: The CLR provides a pool of threads that various classes can use. For example, you can
call methods, read files, or communicate with web services asynchronously, without needing to
explicitly create new threads.

#5: ASP.NET Is Object-Oriented
ASP provides a relatively feeble object model. It provides a small set of objects; these objects are really
just a thin layer over the raw details of HTTP and HTML. On the other hand, ASP.NET is truly object
oriented. Not only does your code have full access to all objects in the .NET Framework, but you can also
exploit all the conventions of an OOP (object-oriented programming) environment. For example, you
can create reusable classes, standardize code with interfaces, extend existing classes with inheritance,
and bundle useful functionality in a distributable, compiled component.

One of the best examples of object-oriented thinking in ASP.NET is found in server-based controls.
Server-based controls are the epitome of encapsulation. Developers can manipulate control objects
programmatically using code to customize their appearance, provide data to display, and even react to
events. The low-level HTML markup that these controls render is hidden away behind the scenes.

Instead of forcing the developer to write raw HTML manually, the control objects render themselves to
HTML just before the web server sends the page to the client. In this way, ASP.NET offers server controls
as a way to abstract the low-level details of HTML and HTTP programming.

Here’s a quick example with a standard HTML text box that you can define in an ASP.NET web page:
<input type="text" id="myText" runat="server" />

With the addition of the runat="server" attribute, this static piece of HTML becomes a fully functional
server-side control that you can manipulate in C# code. You can now work with events that it generates,
set attributes, and bind it to a data source. For example, you can set the text of this box when the page
first loads using the following C# code:

void Page_Load(object sender, EventArgs e)
{
myText.Value = "Hello World!";
}

Technically, this code sets the Value property of an HtmlInputText object. The end result is that a string
of text appears in a text box on the HTML page that’s rendered and sent to the client.

HTML Controls VS. Web Controls

When ASP.NET was first created, two schools of thought existed. Some ASP.NET developers were most
interested in server-side controls that matched the existing set of HTML controls exactly. This approach
allows you to create ASP.NET web-page interfaces in dedicated HTML editors, and it provides a quick
migration path for existing ASP pages. However, another set of ASP.NET developers saw the promise of
something more—rich server-side controls that didn’t just emulate individual HTML tags. These controls
might render their interface from dozens of distinct HTML elements while still providing a simple
objectbased interface to the programmer. Using this model, developers could work with programmable
menus, calendars, data lists, validators, and so on.

After some deliberation, Microsoft decided to provide both models. You’ve already seen an example of
HTML server controls, which map directly to the basic set of HTML tags. Along with these are ASP.NET
web controls, which provide a higher level of abstraction and more functionality. In most cases, you’ll
use HTML server-side controls for backward compatibility and quick migration, and use web controls for
new projects.

ASP.NET web control tags always start with the prefix asp: followed by the class name. For example, the
following snippet creates a text box and a check box:

<asp:TextBox id="myASPText" Text="Hello ASP.NET TextBox" runat="server" />
<asp:CheckBox id="myASPCheck" Text="My CheckBox" runat="server" />
Again, you can interact with these controls in your code, as follows:
myASPText.Text = "New text";
myASPCheck.Text = "Check me!";

Notice that the Value property you saw with the HTML control has been replaced with a Text property.
The HtmlInputText.Value property was named to match the underlying value attribute in the HTML

<input> tag. However, web controls don’t place the same emphasis on correlating with HTML syntax, so
the more descriptive property name Text is used instead.

The ASP.NET family of web controls includes complex rendered controls (such as the Calendar and
TreeView), along with more streamlined controls (such as TextBox, Label, and Button), which map
closely to existing HTML tags. In the latter case, the HTML server-side control and the ASP.NET web
control variants provide similar functionality, although the web controls tend to expose a more
standardized, streamlined interface. This makes the web controls easy to learn, and it also means
they’re a natural fit for Windows developers moving to the world of the Web, because many of the
property names are similar to the corresponding Windows controls.

#6: ASP.NET supports all Browsers
One of the greatest challenges web developers face is the wide variety of browsers they need to
support. Different browsers, versions, and configurations differ in their support of XHTML, CSS, and
JavaScript. Web developers need to choose whether they should render their content according to the
lowest common denominator, and whether they should add ugly hacks to deal with well-known quirks
on popular browsers.

ASP.NET addresses this problem in a remarkably intelligent way. Although you can retrieve information
about the client browser and its capabilities in an ASP.NET page, ASP.NET actually encourages
developers to ignore these considerations and use a rich suite of web server controls. These server
controls render their markup adaptively by taking the client’s capabilities into account. One example is
ASP.NET’s validation controls, which use JavaScript and DHTML (Dynamic HTML) to enhance their
behavior if the client supports it. Another example is the set of Ajax-enabled controls, which uses
complex JavaScript routines that test browser versions and use carefully tested workarounds to ensure
consistent behavior. These features are optional, but they demonstrate how intelligent controls can
make the most of cutting-edge browsers without shutting out other clients. Best of all, you don’t need
any extra coding work to support both types of client.

#7: ASP.NET Is Easy to Deploy and Configure

One of the biggest headaches a web developer faces during a development cycle is deploying a
completed application to a production server. Not only do the web-page files, databases, and
components need to be transferred, but components need to be registered and a slew of configuration
settings need to be re-created. ASP.NET simplifies this process considerably.

Every installation of the .NET Framework provides the same core classes. As a result, deploying an
ASP.NET application is relatively simple. For no-frills deployment, you simply need to copy all the files to
a virtual directory on a production server (using an FTP program or even a command-line command like
XCOPY). As long as the host machine has the .NET Framework, there are no time-consuming registration
steps. Chapter 18 covers deployment in detail.

Distributing the components your application uses is just as easy. All you need to do is copy the
component assemblies along with your website files when you deploy your web application. Because all
the information about your component is stored directly in the assembly file metadata, there’s no need
to launch a registration program or modify the Windows registry. As long as you place these

components in the correct place (the Bin subdirectory of the web application directory), the ASP.NET
engine automatically detects them and makes them available to your web-page code. Try that with a
traditional COM component!

Configuration is another challenge with application deployment, particularly if you need to transfer
security information such as user accounts and user privileges. ASP.NET makes this deployment process
easier by minimizing the dependence on settings in IIS (Internet Information Services). Instead, most
ASP.NET settings are stored in a dedicated web.config file. The web.config file is placed in the same
directory as your web pages. It contains a hierarchical grouping of application settings stored in an easily
readable XML format that you can edit using nothing more than a text editor such as Notepad. When
you modify an application setting, ASP.NET notices that change and smoothly restarts the application in
a new application domain (keeping the existing application domain alive long enough to finish
processing any outstanding requests). The web.config file is never locked, so it can be updated at any
time.

The seven pillars of aspnet

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