Beginners Introduction to ASP.NET

I have seen many tutorials on ASP.NET but most of them starts with coding and writing your first ASP.NET Program. But here I has written this tutorial for explaining why there is a need for ASP.NET when classy ASP is working fine and what are the underlying technology behind ASP.NET, What programming model ASP.NET Provides to programmers. Now let us get started.

ASP.NET is the new offering for Web developers from the Microsoft .It is not simply the next-generation of ASP; in fact, it is a completely re-engineered and enhanced technology that offers much, much more than traditional ASP and can increase productivity significantly.

Because it has evolved from ASP, ASP.NET looks very similar to its predecessor—but only at first sight. Some items look very familiar, and they remind us of ASP. But concepts like Web Forms, Web Services, or Server Controls gives ASP.NET the power to build real Web applications.
Looking Back : Active Server Pages (ASP)

Microsoft Active Server Pages (ASP) is a server-side scripting technology. ASP is a technology that Microsoft created to ease the development of interactive Web applications. With ASP you can use client-side scripts as well as server-side scripts. Maybe you want to validate user input or access a database. ASP provides solutions for transaction processing and managing session state. Asp is one of the most successful language used in web development.
Problems with Traditional ASP

There are many problems with ASP if you think of needs for Today's powerful Web applications.

1. Interpreted and Loosely-Typed Code
ASP scripting code is usually written in languages such as JScript or VBScript. The script-execution engine that Active Server Pages relies on interprets code line by line, every time the page is called. In addition, although variables are supported, they are all loosely typed as variants and bound to particular types only when the code is run. Both these factors impede performance, and late binding of types makes it harder to catch errors when you are writing code.

2. Mixes layout (HTML) and logic (scripting code)
ASP files frequently combine script code with HTML. This results in ASP scripts that are lengthy, difficult to read, and switch frequently between code and HTML. The interspersion of HTML with ASP code is particularly problematic for larger web applications, where content must be kept separate from business logic.

3. Limited Development and Debugging Tools
Microsoft Visual InterDev, Macromedia Visual UltraDev, and other tools have attempted to increase the productivity of ASP programmers by providing graphical development environments. However, these tools never achieved the ease of use or the level of acceptance achieved by Microsoft Windows application development tools, such as Visual Basic or Microsoft Access. ASP developers still rely heavily or exclusively on Notepad.

Debugging is an unavoidable part of any software development process, and the debugging tools for ASP have been minimal. Most ASP programmers
resort to embedding temporary Response. Write statements in their code to trace the progress of its execution.

4. No real state management
Session state is only maintained if the client browser supports cookies. Session state information can only be held by using the ASP Session object. And you have to implement additional code if you, for example, want to identify a user.

5. Update files only when server is down
If your Web application makes use of components, copying new files to your application should only be done when the Web server is stopped. Otherwise it is like pulling the rug from under your application's feet, because the components may be in use (and locked) and must be registered.

6. Obscure Configuration Settings
The configuration information for an ASP web application (such as session state and server timeouts) is stored in the IIS metabase. Because the metabase is stored in a proprietary format, it can only be modified on the server machine with utilities such as the Internet Service Manager. With limited support for programmatically manipulating or extracting these settings, it is often an arduous task to port an ASP application from one server to another.

Introducing ASP.NET

ASP.NET was developed in direct response to the problems that developers had with classic ASP. Since ASP is in such wide use, however, Microsoft ensured that ASP scripts execute without modification on a machine with the .NET Framework (the ASP engine, ASP.DLL, is not modified when installing the .NET Framework). Thus, IIS can house both ASP and ASP.NET scripts on the same machine.
Advantages of ASP.NET

1. Separation of Code from HTML
To make a clean sweep, with ASP.NET you have the ability to completely separate layout and business logic. This makes it much easier for teams of programmers and designers to collaborate efficiently. This makes it much easier for teams of programmers and designers to collaborate efficiently.

2. Support for compiled languages
developer can use VB.NET and access features such as strong typing and object-oriented programming. Using compiled languages also means that ASP.NET pages do not suffer the performance penalties associated with interpreted code. ASP.NET pages are precompiled to byte-code and Just In Time (JIT) compiled when first requested. Subsequent requests are directed to the fully compiled code, which is cached until the source changes.

3. Use services provided by the .NET Framework
The .NET Framework provides class libraries that can be used by your application. Some of the key classes help you with input/output, access to operating system services, data access, or even debugging. We will go into more detail on some of them in this module.

4. Graphical Development Environment
Visual Studio .NET provides a very rich development environment for Web
developers. You can drag and drop controls and set properties the way you do in Visual Basic 6. And you have full IntelliSense support, not only for your code, but also for HTML and XML.

5. State management
To refer to the problems mentioned before, ASP.NET provides solutions for session and application state management. State information can, for example, be kept in memory or stored in a database. It can be shared across Web farms, and state information can be recovered, even if the server fails or the connection breaks down.

6. Update files while the server is running!
Components of your application can be updated while the server is online and clients are connected. The Framework will use the new files as soon as they are copied to the application. Removed or old files that are still in use are kept in memory until the clients have finished.

7. XML-Based Configuration Files
Configuration settings in ASP.NET are stored in XML files that you can easily read and edit. You can also easily copy these to another server, along with the other files that comprise your application.

ASP.NET Overview

Here are some point that gives the quick overview of ASP.NET.

* ASP.NET provides services to allow the creation, deployment, and execution of Web Applications and Web Services
* Like ASP, ASP.NET is a server-side technology
* Web Applications are built using Web Forms. ASP.NET comes with built-in Web Forms controls, which are responsible for generating the user interface. They mirror typical HTML widgets like text boxes or buttons. If these controls do not fit your needs, you are free to create your own user controls.
* Web Forms are designed to make building web-based applications as easy as building Visual Basic applications

Quick Start :To ASP.NET

After this short excursion with some background information on the .NET Framework, we will now focus on ASP.NET.
File name extensions

Web applications written with ASP.NET will consist of many files with different file name extensions. The most common are listed here. Native ASP.NET files by default have the extension .aspx (which is, of course, an extension to .asp) or .ascx. Web Services normally have the extension .asmx.

Your file names containing the business logic will depend on the language you use. So, for example, a C# file would have the extension .aspx.cs. You already learned about the configuration file Web.Config.

Another one worth mentioning is the ASP.NET application file Global.asax - in the ASP world formerly known as Global.asa. But now there is also a code behind file Global.asax.vb, for example, if the file contains Visual Basic.NET code. Global.asax is an optional file that resides in the root directory of your application, and it contains global logic for your application.
All of these are text files

All of these files are text files, and therefore human readable and writeable.
The easiest way to start

The easiest way to start with ASP.NET is to take a simple ASP page and change the file name extension to .aspx.
Page Syntax

Here is quick introduction of syntax used in ASP.NET
Directives

You can use directives to specify optional settings used by the page compiler when processing ASP.NET files. For each directive you can set different attributes. One example is the language directive at the beginning of a page defining the default programming language.
Code Declaration Blocks

Code declaration blocks are lines of code enclosed in tags. They contain the runat=server attribute, which tells ASP.NET that these controls can be accessed on the server and on the client. Optionally you can specify the language for the block. The code block itself consists of the definition of member variables and methods.
Code Render Blocks

Render blocks contain inline code or inline expressions enclosed by the character sequences shown here. The language used inside those blocks could be specified through a directive like the one shown before.
HTML Control Syntax

You can declare several standard HTML elements as HTML server controls. Use the element as you are familiar with in HTML and add the attribute runat=server. This causes the HTML element to be treated as a server control. It is now programmatically accessible by using a unique ID. HTML server controls must reside within a section that also has the attribute runat=server.
Custom Control Syntax

There are two different kinds of custom controls. On the one hand there are the controls that ship with .NET, and on the other hand you can create your own custom controls. Using custom server controls is the best way to encapsulate common programmatic functionality.

Just specify elements as you did with HTML elements, but add a tag prefix, which is an alias for the fully qualified namespace of the control. Again you must include the runat=server attribute. If you want to get programmatic access to the control, just add an Id attribute.

You can include properties for each server control to characterize its behavior. For example, you can set the maximum length of a TextBox. Those properties might have sub properties; you know this principle from HTML. Now you have the ability to specify, for example, the size and type of the font you use (font-size and font-type).

The last attribute is dedicated to event binding. This can be used to bind the control to a specific event. If you implement your own method MyClick, this method will be executed when the corresponding button is clicked if you use the server control event binding shown in the slide.
Data Binding Expression

You can create bindings between server controls and data sources. The data binding expression is enclosed by the character sequences . The data-binding model provided by ASP.NET is hierarchical. That means you can create bindings between server control properties and superior data sources.
Server-side Object Tags

If you need to create an instance of an object on the server, use server-side object tags. When the page is compiled, an instance of the specified object is created. To specify the object use the identifier attribute. You can declare (and instantiate) .NET objects using class as the identifier, and COM objects using either progid or classid.
Server-side Include Directives

With server-side include directives you can include raw contents of a file anywhere in your ASP.NET file. Specify the type of the path to filename with the pathtype attribute. Use either File, when specifying a relative path, or Virtual, when using a full virtual path.
Server-side Comments

To prevent server code from executing, use these character sequences to comment it out. You can comment out full blocks - not just single lines.