ASP.NET

Active Server Pages (ASP), also known as Classic ASP, was introduced in 1998 as Microsoft's first server side scripting engine. ASP is a technology that enables scripts in web pages to be executed by an Internet server. ASP pages have the file extension .asp, and are normally written in VBScript.

ASP.NET is a new ASP generation. It is not compatible with Classic ASP, but ASP.NET may include Classic ASP. ASP.NET pages are compiled, which makes them faster than Classic ASP. ASP.NET has better language support, a large set of user controls, XML-based components, and integrated user authentication. ASP.NET pages have the extension .aspx, and are normally written in VB (Visual Basic) or C# (C sharp). User controls in ASP.NET can be written in different languages, including C++ and Java. When a browser requests an ASP.NET file, the ASP.NET engine reads the file, compiles and executes the scripts in the file, and returns the result to the browser as plain HTML.

ASP.NET Programming Languages

ASP.NET Programming Languages is two types

1. Visual Basic (VB.NET)

2. C# (Pronounced C sharp)

When you enter Visual Basic code, you must be aware of the two coding rules as summarized below. First, you must separate the words in each statement by one or more spaces. Note, however, that you don’t have to use spaces to separate the words from operators, although Visual Basic adds spaces for you by default.

1. Use spaces to separate the words in each statement.
2. To continue a statement to the next line, you can type a space followed by an under- score (the line-continuation character). In the cases listed below, you can continue a statement without using a line-continuation character.

Second, if you want to continue a statement, you can do that by coding a space followed by a line-continuation character, which is an underscore U. Starting with Visual Basic 2010, though, you can often continue a line without using the line-continuation character.

ASP.NET is a web development platform, which provides a programming model, a comprehensive software infrastructure and various services required to build up robust web applications for PC, as well as mobile devices. ASP.NET works on top of the HTTP protocol, and uses the HTTP commands and policies to set a browser-to-server bilateral communication and cooperation.

ASP.NET is a part of Microsoft .Net platform. ASP.NET applications are compiled codes, written using the extensible and reusable components or objects present in .Net framework. These codes can use the entire hierarchy of classes in .Net framework.

ASP.NET Web Forms Model

ASP.NET web forms extend the event-driven model of interaction to the web applications. The browser submits a web form to the web server and the server returns a full markup page or HTML page in response. All client side user activities are forwarded to the server for stateful processing. The server processes the output of the client actions and triggers the reactions. Now, HTTP is a stateless protocol. ASP.NET framework helps in storing the information regarding the state of the application, which consists of:

1. Page state

2. Session state

The page state is the state of the client, i.e., the content of various input fields in the web form. The session state is the collective information obtained from various pages the user visited and worked with, i.e., the overall session state. To clear the concept, let us take an example of a shopping cart.

User adds items to a shopping cart. Items are selected from a page, say the items page, and the total collected items and price are shown on a different page, say the cart page. Only HTTP cannot keep track of all the information coming from various pages. ASP.NET session state and server side infrastructure keeps track of the information collected globally over a session.

The ASP.NET runtime carries the page state to and from the server across page requests while generating ASP.NET runtime codes, and incorporates the state of the server side components in hidden fields.

The Visual Studio IDE

The new project window allows choosing an application template from the available templates. When you start a new web site, ASP.NET provides the starting folders and files for the site, including two files for the first web form of the site.

The file named Default.aspx contains the HTML and asp code that defines the form, and the file named Default.aspx.cs (for C# coding) or the file named Default.aspx.vb (for VB coding) contains the code in the language you have chosen and this code is responsible for the actions performed on a form.

The primary window in the Visual Studio IDE is the Web Forms Designer window. Other supporting windows are the Toolbox, the Solution Explorer, and the Properties window. You use the designer to design a web form, to add code to the control on the form so that the form works according to your need, you use the code editor.

ASP.NET Application Life Cycle

1. User makes a request for accessing application resource, a page. Browser sends this request to the web server.

2. A unified pipeline receives the first request and the following events take place:
i. An object of the class ApplicationManager is created.
ii. An object of the class HostingEnvironment is created to provide information regarding the resources.
iii. Top level items in the application are compiled.

3. Response objects are created. The application objects such as HttpContext, HttpRequest and HttpResponse are created and initialized.

4. An instance of the HttpApplication object is created and assigned to the request.

5. The request is processed by the HttpApplication class. Different events are raised by this class for processing the request.

The MVC Programming Model

MVC is one of three ASP.NET programming models.

MVC is a framework for building web applications using a MVC (Model View Controller) design:

1. The Model represents the application core (for instance a list of database records).
2. The View displays the data (the database records).
3. The Controller handles the input (to the database records).

The MVC model also provides full control over HTML, CSS, and JavaScript.

The MVC model defines web applications with 3 logic layers:

The business layer (Model logic)
The display layer (View logic)
The input control (Controller logic)

The Model is the part of the application that handles the logic for the application data. Often model objects retrieve data (and store data) from a database.

The View is the parts of the application that handles the display of the data. Most often the views are created from the model data.

The Controller is the part of the application that handles user interaction. Typically controllers read data from a view, control user input, and send input data to the model.

The MVC separation helps you manage complex applications, because you can focus on one aspect a time. For example, you can focus on the view without depending on the business logic. It also makes it easier to test an application.

The MVC separation also simplifies group development. Different developers can work on the view, the controller logic, and the business logic in parallel.

Creating the Web Application

In the New Project dialog box:.

Open the Visual C# templates
Select the template ASP.NET MVC 3 Web Application
Set the project name to MvcDemo
Set the disk location to something like c:\w3schools_demo
Click OK