ASP.NET - Web Programming

Introduction to ASP.NET
Web programming
Week 11, day2

ASP.NET Overview & Features
 ASP.NET provides services to allow the creation, deployment, and
execution of
Web Applications and Web Services
 Web Applications are built using Web Forms
 Built on .NET Framework: any .NET programming language can be
used (C#, Visual Basic)
 Complete object model
 Separation of code and UI
 Maintains page state
 Session management

ASP.NET with HTML
• separation between markup and code - .aspx & .aspx.vb/ .aspx.cs
files
•Inline asp code can be inserted inside HTML as in case of PHP with
“<% ‘this is asp.net code %>” tags
•Double clicking on each control generates the most used event
handler for that control in the code behind file
•The page directive
•The runat = “server” attribute for server controls

Lets jump into coding
An example application

This is intented to walk you through creating a simple application using asp.net,
visual studio an C#
The application takes the time from the web server and shows it on an aspx page
To create a new application follow the steps in the previous tutorial(ppt)
Following the instructions in the previous tutorial create a new C# application
named ‚webtime‛ in visual studio.
an ASPX file (i.e., Web Form), default named Default.aspx is created for each new
project.
Visual Web Developer creates a code-behind file named Default.aspx.cs.
Example Application - Webtime

• the solution explorer inside visual studio shows the folder structure of your
project and the toolbox shows a list of available .net controls those can be added to
your webpage. (Please explore the ‚view‛ tab if any or both of these are not
shown in the VS window)
•When the project loads for the first time, the Web Forms Designer displays the
auto generated ASPX file in Source mode.
•Design mode indicates the XHTML element where the cursor is currently
located.
•You can also view both the markup and the web-page design at the same time by
using Split mode
•Right click the ASPX file in the Solution Explorer and select View Code to open
the code-behind file.
Renaming and editing the aspx file

Let’s create our first ASP.NET page using Visual Studio
1. Modify title of the page
2. Add a heading <h2>
3. Look at the page in Design and Split modes
4. Add a Label control from the Toolbox
5. Change ID of the Label control
6. Change some physical properties of the Label control
7. Go to Default.aspx.cs file and add Page_Init function to set Text property of
the Label control
Editing & adding controls to the aspx file

Changing the Title of the Page
•We change the page’s title from the default Untitled Page to A Simple Web Form
•Open the ASPX file in Source mode and modify the text between the <title> tags.
•Alternatively, you can modify the Web Form’s Title property in the Properties
window.
•To view the Web Form’s properties, select DOCUMENT from the drop-down list in
the Properties window.
Designing the Page
•To add controls to the page, you can drag and drop them from the Toolbox onto the
Web Form in Design mode.
•Like the Web Form itself, each control is an object that has properties, methods and
events.
•You can type text directly on a Web Form at the cursor location or insert XHTML
elements using menu commands.

Renaming the ASPX File
 Right click the ASPX file in the Solution Explorer and select Rename.
 Enter the new file name WebTime.aspx and press Enter. Both the ASPX file and the
code-behind file are updated.
Renaming the Class in the Code-Behind File and Updating the ASPX File
Visual Studio’s refactoring tool, automatically updates the existing references to this
class in the rest of the project to reflect this change.
Check the ‚code file‛ attribute in the page directive in the .aspx file for correctness
(it should have the new file name)

Visual Studio generates the markup shown when you create the GUI.
11
1 <%-- WebTime.aspx --%>
2 <%-- A page that displays the current time in a Label. --%>
3 <%@ Page Language="C#" AutoEventWireup="true"
CodeFile="WebTime.aspx.cs"
4 Inherits="WebTime" EnableSessionState="False" %>
5
6 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
7 "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
8
9 <html xmlns="http://www.w3.org/1999/xhtml">
10 <head runat="server">
11 <title>A Simple Web Form Example</title>
12 </head>
13 <body>
14 <form id="form1" runat="server">
15 <div>
16 <h2>Current time on the web server:</h2>
ASP.NET comments
begin with <%-- and
terminate with --%>,
and can span multiple
lines.
The Page directive
specifies information
needed by ASP.NET
to process this file.
ASPX file that displays the web server’s time.
The document type
declaration, which specifies
the document element name
and the PUBLIC URI for the
DTD that defines the
XHTML vocabulary.
XHTML documents
have the root element
html and markup
information about the
document in the head
element.
The body contains
the main content
that the browser
displays.
The form that contains our
XHTML text and controls is set
to execute on the server, which
generates equivalent XHTML.

Visual Studio generates the markup shown when you create the GUI.
17 <p>
18 <asp:Label ID="timeLabel" runat="server" BackColor="Black"
19 Font-Size="XX-Large" ForeColor="Yellow"
20 EnableViewState="False"></asp:Label>
21 </p>
22 </div>
23 </form>
24 </body>
25 </html>
Markup for a label
web control.The asp: tag prefix
indicates that the
label is an ASP.NET
web control, not an
XHTML element.
• In an ASPX file a directive is delimited by <%@ and %>.

Examining the aspx file
• The Page directive’s Language attribute specifies the
code-behind file’s language.
• The CodeFile attribute specifies the code-behind filename.
• When AutoEventWireup is true, ASP.NET automatically treats a method of
name Page_eventName as an event handler.
• When AutoEvent-Wireup is set to false, you specify event handlers using
attributes in the Page directive just as you would any other web control.
• The Inherits attribute (line 4) specifies the class in the code-behind file from
which this ASP.NET class inherits.

Examining the aspx file
• Setting the runat attribute to "server" indicates that ASP.NET processes the
element and its nested elements and generates the corresponding XHTML.
• The body contains the main content that the browser displays.
• The form that contains our XHTML text and controls is set to execute on
the server, which generates equivalent XHTML.
• The ID attribute assigns a name to a control, used as an identifier in the
code-behind file.
• The asp: tag prefix indicates that the label is an ASP.NET web control, not
an XHTML element.
• Each web control maps to a corresponding XHTML element or group of
elements.

The code-behind file (WebTime.aspx.cs)
1 // WebTime.aspx.cs
2 // Code-behind file for a page that displays the current time.
3 using System;
4
5 public partial class WebTime : System.Web.UI.Page
6 {
7 // initializes the contents of the page
8 protected void Page_Init( object sender, EventArgs e )
9 {
10 // display the server's current time in timeLabel
11 timeLabel.Text = DateTime.Now.ToString( "hh:mm:ss" );
12 } // end method Page_Init
13 } // end class WebTime
Code-behind file for a page that displays
the web server’s time. (Part 1 of 2.)
The Page_Init
method handles the
page’s Init event,
which indicates that
the page is ready to
be initialized.
Retrieve the current
time and formats it
as hh:mm:ss.

WebTime.aspx Example run
• The Page_Init method handles the page’s Init event, which indicates
that the page is ready to be initialized.

Relationship Between an ASPX File and a
Code Behind File
• The code-behind file inherits from Page, which defines the general
functionality of a web page.
• The code-behind file contains a partial class.
• The first time the web page is requested, this class is compiled, and an
instance is created.
• This instance represents our page—it creates the XHTML that is sent to the
client.

How the Code in an ASP.NET Web Page Executes
When an instance of the page is created, the PreInit event occurs first,
invoking method Page_PreInit, which can be used to set a page’s theme.
The Init event occurs next, invoking method Page_Init, which is used to
initialize objects and other aspects of the page.
Next, the Load event occurs, and the Page_Load event handler executes.
 The Init event is raised only once (when the page is first requested).
 The Load event is raised with every request.
 The page then processes any events that are generated by the page’s controls.
 Once a response has been generated and sent, an Unload event occurs,
which calls Page_Unload, which typically releases resources used by the
page.

How HTML is rendered by asp.net
• To view the XHTML generated by ASP.NET, select View Source option in
the browser
• Nonvisual form components, called hidden inputs, store data that the user
doesn’t need to see.
• Attribute method of the form element specifies the request method (usually
get or post). The action attribute identifies the resource that will be
requested when a form is submitted.

XHTML generated by ASP.NET when a web browser
requests WebTime.aspx.
1 
2 
3 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
4 "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
5
6 <html xmlns="http://www.w3.org/1999/xhtml">
7 <head>
8 <title>A Simple Web Form Example</title>
9 </head>
10 <body>
11 <form method="post" action="WebTime.aspx" id="form1">
12 <div>
13 <input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value=
14 "/wEPDwUJODExMDE5NzY5ZGQ4n4mht8D7Eqxn73tM5LDnstPlCg==" />
15 </div>
Nonvisual form
components,
called hidden
inputs, store data
that the user
doesn’t need to
see.
Attribute method
of the form
element specifies
the request method
(usually get or
post). The
action attribute
identifies the
resource that will
be requested when
a form is
submitted.

XHTML generated by ASP.NET when a web browser
requests WebTime.aspx.
16
17 <div>
18 <h2>Current time on the web server:</h2>
19 <p>
20 <span id="timeLabel" style="color:Yellow;
21 background-color:Black;font-size:XX-Large;">
22 03:11:49
23 </span>
24 </p>
25 </div>
26 </form>
27 </body>
28 </html>
The form contains a
span element to
represent the text in
the label. Formatting
properties of time
Label are converted
into the style
attribute of the span
element.

Running the program
• You can view the Web Form several ways.
– You can select Debug > Start Without Debugging, which runs the
application by opening it in a browser window.
– To debug your application, you can select Debug > Start Debugging.
You cannot debug a web application unless debugging is explicitly
enabled by the web.config file.
– To view a specific ASPX file, you can right click either the Web Forms
Designer or the ASPX file name and select View In Browser.
– Finally, you can run your application by opening a browser window and
typing the web page’s URL in the Address field.

Event handling
• GUIs are event driven.
• When the user interacts with a GUI component, a corresponding event is
raised (eg. Click of a button)
• A method that performs a task in response to an event is called an event
handler.

Event handling example
• Let’s create another ASP.NET page using Visual Studio
1. Add a Button and a Label control (label id = labelHello)
2. To create this click event handler, double click the Button on the Form.
3. The following empty event handler is declared:
4. Set the Text property of the Label control with the current time in this
function.
protected void Button1_Click(object sender, EventArgs e)
{
labelHello.Text = "Hello World! Time is " + DateTime.Now;
}
‘Where Button1 is the unique id of the element

Event handling example
• To add an event handler, alternatively in markup (aspx) file:
1. Add a onclick="BClick" property to the Button control.
2. Add a function BClick to the page class in the code behind.

Event handling
• By convention, C# names the event-handler method as
objectName_eventName (e.g., Button1_Click).
• Each event handler receives two parameters when it is called:
– An object reference named sender—a reference to the object that
generated the event.
– A reference to an object of type EventArgs, which contains additional
information about the event.
• Typically, controls can generate many different types of events.
• Clicking the Events icon (the lightning-bolt icon) in the Properties window,
displays all the events for the selected control.

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ASP.NET - Web Programming

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