ASP.NET Web Forms

Web Forms

Web Forms are based on ASP.NET. Working with Web Forms is similar to working with Windows Forms. But the difference is that we will create Web pages with Web forms that will be accessible by a Web browser. Web Forms are Web pages that serve as the user interface for a Web application. A Web Forms page presents information to the user in any browser or client device and implements application logic using server-side code. Web Forms are based on the System.Web.UI.Page class. The class hierarchy for the page class is shown below.

Object
  Control
   TemplateControl
    Page

Components of Web Forms

In Web Forms pages, the user interface programming is divided into two parts: the visual component (design page) and the logic (code behind page).

The visual element is the Web Forms page. The page consists of a file with static HTML, or ASP.NET server controls, or both simultaneously. The Web Forms page works as a container for the static text and the controls we want to display. Using the Visual Studio Web Forms Designer and ASP.NET server controls, we can design the form just like in any Visual Studio application.

The logic for the Web Forms page consists of code that we create to interact with the form. The programming logic is in a separate file from the user interface file. This file is the "code-behind" file and has an ".aspx.vb" (VB) or ".aspx.cs" (C-Sharp) extension. The logic we write in the code-behind file can be written in Visual Basic or Visual C#.

The code-behind class files for all Web Forms pages in a project are compiled into the project dynamic-link library (.dll) file. The .aspx page file is also compiled, but differently. The first time a user loads the aspx page, ASP.NET automatically generates a .NET class file that represents the page, and compiles it to a second .dll file. The generated class for the aspx page inherits from the code-behind class that was compiled into the project .dll file. When the user requests the Web page URL, the .dll files run on the server and dynamically produces the HTML output for your page.

When you open a new ASP.NET Web Application in Visual Studio .NET the form that is loaded (WebForm1.aspx) looks like the image below.

The form opens in design mode and you can switch to HTML view by clicking on the HTML tab. Startvbdotnet.aspx file in the image above is standard HTML with ASP elements embedded in it. The file looks like the image below.

From the above image notice the Codebehind attribute (second line). The codebehind attribute connects this code to the appropriate Visual Basic or C# code (code behind file). Startvbdotnet.aspx.vb, the codebehind file for Startvbdotnet.aspx where you write your logic looks like this:

Public Class Startvbdotnet Inherits System.Web.UI.Page
Protected WithEvents TextBox1 As System.Web.UI.WebControls.TextBox
Protected WithEvents Button1 As System.Web.UI.WebControls.Button
Protected WithEvents Label1 As System.Web.UI.WebControls.Label

#Region " Web Form Designer Generated Code "

'This call is required by the Web Form Designer.
Private Sub InitializeComponent()

End Sub

Private Sub Page_Init(ByVal sender As System.Object, ByVal e As System.EventArgs)_
Handles MyBase.Init
'CODEGEN: This method call is required by the Web Form Designer
'Do not modify it using the code editor.
InitializeComponent()
End Sub

#End Region

Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)_
Handles MyBase.Load
'Put user code to initialize the page here
End Sub

End Class

Notable Properties of Page Object

Below are some notable properties of Page objects:

Application: Gets an application object
ClientTarget: Gets/Sets if you want to override automatic browser capabilities detection and handle page rendering for specific browsers
ErrorPage: Gets/Sets an error page's URL in case there are unhandled page exceptions
IsPostBack: Indicates if a page was created after a client postback or if it is being loaded for the first time
IsValid: Indicates if the page validation was successful
Request: Gets the current http request object
Response: Gets the current http response object
Server: Gets the current server object
Session: Gets the current session object
Site: Gets Web Site data
User: Gets data about the user
Validators: Gets a collection of validation controls on the page

The ASPX Extension

Many of us wonder why the extension for ASP.NET is .aspx. Well, long time ago, when ASP.NET was being developed at Microsoft it was referred to as ASP+ (ASP Plus). You can't use a "+" symbol in a filename but if you turn the + symbol about 45 degrees, it looks like a x. Microsoft chose .aspx as the extension of ASP+. After the name was changed to ASP.NET, Microsoft did'nt change the extension and left it as aspx.