Chapter 9 - Department of Computer Information Systems

CIS 3260 – Intro to Programming in C#
Web Applications
McGraw-Hill
© 2010 The McGraw-Hill Companies, Inc. All rights reserved.
Explain the functions of the server and the
client in Web programming
Create a Web Form and run it in a browser
Describe the differences among the various
types of Web controls and the relationship
of Web controls to controls used on
Windows forms
Understand the event structure required for
Web programs
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Create multiple pages in a Web application
Navigate using the HyperLink control and
the Server object
Validate Web input using the validator
controls
Use state management to preserve values in
variables
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Dr. David McDonald Chapter 9 – Page 1

CIS 3260 – Intro to Programming in C#
Web Forms are used to create the user
interface for Web applications
A Web Form displays as a document in a
browser
You can create documents that display on
mobile devices, such as cell phones and PDAs
(using the Standard Edition and above)
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• Web applications require a server and
a client
– Server sends the Web Pages to the client
– Client displays the Web Pages in a
browser
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To develop Web applications
◦ Use a remote Web server
◦ Make your local machine a Web server
• Visual Studio Web Server
• Installs automatically with Visual Web Developer or Visual
Studio
• Simplifies development, testing, and debugging
• Use IDE tools to transfer application to an IIS Web server
after development to share with others
• Internet Information Services (IIS)
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Dr. David McDonald Chapter 9 – Page 2

CIS 3260 – Intro to Programming in C#
Browsers display pages written in a markup
language such as HTML or XHTML
Pages may also contain program logic
◦ Script
• JavaScript, VBScript, JScript
◦ Java applets
Programming for the Internet
◦ Test and check output on multiple browsers
• Internet Explorer, Mozilla FireFox and Opera
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Web pages are stateless
◦ The page does not store any information about
its contents from one invocation to the next
Techniques for working around the
stateless limitation
◦ Storing cookies on the local machine
◦ Sending state information to the server as part of
the page's address, called the uniform resource
locator (URL)
• The server can send the state information back with the
next version of the page
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ASP.NET 3.5 is the latest Web programming
technology from Microsoft
ASP.NET provides libraries, controls, and
programming support for programs that:
◦ Interact with the user
◦ Maintain state
◦ Render controls
◦ Display data
◦ Generate appropriate HTML
Write object-oriented, event-driven Web
applications using C# and ASP.NET
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Dr. David McDonald Chapter 9 – Page 3

CIS 3260 – Intro to Programming in C#
Each Web Form has two distinct pieces
◦ HTML and instructions needed to render the page
◦ C# code
A Web Form generates two files:
◦ .aspx extension for the HTML
◦ .aspx.cs extension for the C# code
• Holds the logic to respond to events
• Called the "code behind" file
C# code is not compiled into an .exe file, it
is compiled into a dynamic link library (dll)
file located on the server
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IIS on a local computer hosts a Web server
that must be secured
Requires administrative rights on the
computer to create IIS Web projects
By default files are stored in
C:\inetpub\wwwroot folder
◦ A virtual IIS directory can be created to store a Web
site
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Select New Web Site from the File menu
In the New Web Site dialog box, select the
template, location, and language
Give the Web
site a name
by appending
the name to
the location
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Dr. David McDonald Chapter 9 – Page 4

CIS 3260 – Intro to Programming in C#
A new Web site automatically contains one
Web page, Default.aspx
◦ Visual representation of the page (HTML tags)
A second file, Default.aspx.cs, holds the C#
code for the page
ASP.NET has a second model for Web
applications—single-file model
◦ Stores all HTML, control definitions, and code in
one single file
The textbook teaches the code-separation
model that uses two separate files
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Differences between a Web application and
a Windows Forms application
◦ Web Form (page or document) not a Windows
Form
◦ Toolbar
◦ List of files in the Solution Explorer
◦ Toolbox has different controls
• Properties and events different than controls that have a
Windows counterpart
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Three tabs at bottom of Web Form
◦ Design
◦ Split
• Splits the Document window horizontally to see both
the design and source
◦ Source
• Static HTML code
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Dr. David McDonald Chapter 9 – Page 5

CIS 3260 – Intro to Programming in C#
Several types of controls available for Web
Forms
◦ Standard (ASP.NET server controls)—Richest and
most powerful controls provided by ASP.NET and
.NET framework
◦ Data—Display database data
◦ Validation—Validate user input before it is sent to
server
◦ Navigation—Includes the Menu control
◦ Login—Login controls and wizards
◦ WebParts—Change the appearance and behavior
of the interface from the browser
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Web application files differ greatly from a
Windows application
aspx file
◦ Holds specifications for the user interface used by
the server to render pages
aspx.cs file
◦ Code-behind file for the aspx file
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The IDE does not automatically generate the
code necessary for debugging a Web
application
Run without Debugging
◦ Ctrl + F5 or Debug/Start without debugging
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Dr. David McDonald Chapter 9 – Page 6

CIS 3260 – Intro to Programming in C#
If you try to run with debugging (F5), a
message box gives the choice to run
without debugging or add the debugging
code to the Web.config file
◦ Add the following line of code to the Web.config
file to run with debugging
Set breakpoints, single step execution, and
display the contents of variables and
properties at debugging time
Always remove debugging support before
deploying an application
◦ Debugging code slows an application
considerably
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HTML tables contain
rows and columns
and allow control
over placement of
elements on a Web
page
Add controls and text
to the table cells to
align the columns
A table is an HTML
control, which
requires no serverside
programming
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Add controls to any table cell or type text in a
cell during design time
◦ To refer to the text in a cell at run time, add a label
and give it an ID or type text directly into the cell
◦ Merge cells to allow room for a title or a larger
image
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Dr. David McDonald Chapter 9 – Page 7

CIS 3260 – Intro to Programming in C#
Places controls in a specific X and Y
position
◦ Controls may not show up if user has set browser
window to small size
◦ Controls may overlap if the user has selected a
large font size for the browser window
Controls can be dragged using the white
tab at the top of a selected control
Controls remain in the same position
relative to the Web page
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ASP.NET provides several techniques to
navigate from one Web page to another
Easiest form of navigation is to use a
HyperLink control
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Add a HyperLink control to allow the user to
navigate to another page or another site
Set properties of the HyperLink control
◦ Text—Text to display for the user
◦ NavigateUrl—Specify the URL to which to navigate
• For another Web site, type the Web address (URL)
• For another page in the application, use the Select URL
dialog box and select the page from a list
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Dr. David McDonald Chapter 9 – Page 8

CIS 3260 – Intro to Programming in C#
Add a new form to the project
Add controls to the new page
Add a HyperLink to the Main Page
Set the Start Page
Run the application, test the links
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At times a hyperlink cannot be used because
some other action in code needs to be
performed prior to the transfer
Transfer to another page in code
◦ Use the Server.Transfer method
Server.Transfer (“Offer.aspx”);
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ASP.NET provides several validator controls
that can automatically validate input
◦ Add a validator control
◦ Attach it to the controlToValidate (such as a text
box)
A blank entry passes the validation for each
of the controls except the
RequiredFieldValidator
Enter a complete message in the
ErrorMessage property or set the property to
an asterisk
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Dr. David McDonald Chapter 9 – Page 9

CIS 3260 – Intro to Programming in C#
Validator Controls
RequiredFieldValidator
CompareValidator
Requires that the user enter something into the
field
Compares the value in the field to the value in
another control or to a constant. Also can be
used to verify that the input value can be
converted to the correct data type
RangeValidator
RegularExpressionValidator
ValidationSummary
Requires that the input value falls in the specified
range
Validates against a regular expression, similar to
the mask in a masked text box
Displays a summary of all of the messages from
the validator controls
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Web pages hold static data
Each time a page is displayed or redisplayed
it is a fresh copy
Each time the page is posted back to the
server a new copy of the program is loaded
Steps must be taken to maintain the state of
the page
◦ Otherwise the values of variables and controls on
the page will be lost in every postback
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ASP.NET can retain and redisplay control
contents
Web controls have an EnableViewState
property
◦ Set to true by default
◦ Indicates to the server to send the control’s
contents back with the page
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Dr. David McDonald Chapter 9 – Page 10

CIS 3260 – Intro to Programming in C#
Local variables work the same in a Web or
Windows application
Class-level variables are lost unless steps are
taken to save them
Store the value of a class-level variable in a
control on a Web page
◦ EnableViewState property holds the value during
postback
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Set up a control with its Visible property set
to false or use the HiddenField control
Assign the class-level variable to the
invisible control
◦ For a hidden field, use the (string) Value property
// Declare a class level variable.
private decimal discountTotalDecimal;
protected void submitButton_Click(object sender, EventArgs e)
{
// . . . Calculations omitted.
discountHiddenField.Value = discountTotalDecimal.ToString();
}
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The Page_Load event occurs many times
(during each postback) in a Web application
IsPostBack property is set to false for an
initial page load and true for all page loads
following the first
Test for IsPostBack == false to perform
initialization tasks
Test for IsPostBack == true to perform
tasks only on postback
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Dr. David McDonald Chapter 9 – Page 11

CIS 3260 – Intro to Programming in C#
One instance of the Session object exists for
each user of an application
◦ Use to store information about the user on the
server
◦ Each time a user accesses an application, a Session
object is created with a unique SessionID
◦ Session values are maintained as long as the
session exists
• Sessions can time out, terminate or users can logout
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Drawbacks to session objects
◦ Information is stored on server
• Large amounts of data for multiple users can bog
down the server
◦ Web sites split server loads among several systems
(Web Farm)
• State information might be on a different server than
where the postback originates
• .NET handles this problem by specifying the name of the
machine that stores the session values in the Web.config
file
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Use the Contents collection of the Session
object to store values in code
Each item in the collection is a key/value pair
◦ Make up a name (the key) and assign a value
Clear all session variables by using the
Session.Clear method
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Dr. David McDonald Chapter 9 – Page 12