Creating Web applications - I

The C# Coumn - Yashawant Kanetkar

The ASP.NET technology is used to create Web applications and dynamic websites. ASP.NET is compatible and is integrated with the .NET environment. It is rather different from ASP. First let’s take a look at what the differences are.

ASP (Active Server Pages) is technology that enables the dynamic creation of Web pages. An ASP page is an HTML file with server-side script written in VBScript or JScript. When a client requests an ASP page, the Web server delivers the static HTML portions of the page without any modification, and processes the server-side script, which further generates HTML. The problems faced with ASP are:

• (a) The scripting is interpreted, leading to slow rendering of pages.
• (b) The entire HTML portion (content) and scripting portion (code) is jumbled up in one ‘.asp’ file.
• (c) ASP code has to be written for everything, including simple jobs like validating form fields.

ASP.NET solves all these problems faced with ASP. First of all, ASP.NET pages are compiled and not interpreted. Secondly, ASP.NET pages are structured, meaning that server-side scripts and plain HTML are not jumbled upscripts and HTML can be separated. ASP.NET provides a feature called code-behind. With this feature, the server-side code of a page can be separated and placed into another file. A ‘.aspx’ file contains the HTML portion of the application and a ‘.cs’ file contains the code. This allows one part of the development team to concentrate on HTML design, while others work on the code.

Web Forms
.NET Web Applications or Web Forms like WinForms bring the concept of Rapid Application Development (RAD) to Web application creation. Web forms are created by dropping controls onto a form and then double-clicking those controls and writing event handlers for them in code-behind pages. The controls to be used in Web Forms are present in the .NET Framework class library. Some controls are mere wrappers around simple HTML tags, but others represent complex UI objects that generate HTML. Let us first build a Web Form and then understand the working of an ASP.NET Web Form application.

In this article, we shall create a registration form for students to register for an online course. To start with, create an ASP.NET application named ‘Registration’ by selecting ASP.NET Web Application from the template list. On doing so, a virtual directory named Registration would get created in the IIS and its local location will be ‘C:\Inetpub\wwwroot\Registration’. As soon as we create a project, the following files would get generated in the Registration directory:

• A Global.asax file containing application-level program directives, handlers for application and session-level events, and declarations of objects that are globally accessible to all parts of the application.
• A Web.config file containing XML that stores the application configuration information.
• A WebForm1.aspx file containing HTML for rendering Web Forms.
• A WebForm1.aspx.cs file containing the code-behind page written in C#.NET.
• An AssemblyInfo.cs file containing standard code for assembly description.
• A WebForm1.disco file describing any Web services in the project.

We will only be concentrating on the ‘WebForm1.aspx’ file (content) and the ‘WebForm1.aspx.cs’ (code) file for our application.

On creating the application, an empty Web form gets displayed in the design view of the ‘WebForm1.aspx’ file. We intend to add a table to this form. To add a table we need to select the Table menu and then the ‘Insert | Table’ option. We are now presented with the ‘Insert Table’ Dialog box. Select the rows (11) and columns (3) that we wish to add to the table. A grid gets displayed on the form. Insert the controls—labels, text boxes, validation controls and button to the form as shown in the following figure.

The details of the controls are given in the following table.

The controls appearing in red are called validation controls. Whenever we enter something on the form and submit it to the server it is called a postback. Validation controls provide a method of validating user input without writing any code. Whenever postback is initiated (i.e. we click the ‘Submit Form’ button) each control checks the control it is validating and changes its IsValid property accordingly.

If the property is set to false, it means that the user input is wrong. In such a case an error message is flashed. If the property is set to true, the postback occurs. Some of the validation controls that we have used in this program are given in the following table.

The pass textbox would accept a password. Generally a password is something that should not be visible, hence we need to change the TextMode property of this textbox to Password. Now, whatever the student types in, this textbox is substituted by asterisks (*).

We must now change the properties of validation controls. But that’s for next time.

Yashavant Kanetkar, one of the first Express Computer columnists, is an established software expert, speaker and author with several best-sellers to his credit, including titles like “Let Us C” and the “Fundas” series. Contact him at kanet@nagpur.dot.net.in