02 asp.net session02

of 19
Developing Web Applications Using ASP.NET
In this session, you will learn to:
Describe various event-handling techniques
Explain how to detect browser types and capabilities
Explain how to access page headers
Describe how to handle page-level errors and application-level
errors
Implement advanced techniques for handling events
Implement browser-capability detection
Implement page-header manipulation
Implement page-level and application-level error handling
Objectives

of 19
ASP.NET provides you with a flexible framework that enables
you to work with event handlers in several ways.
The various approaches that can be used to work with the
event handlers include:
Using default events
Using non-default events
Using the AutoEventWireup capabilities of a Web form to
associate events and event-handling methods
Creating centralized event-handling methods to respond to
multiple events
Event Handling in Web Applications

of 19
Default and Non-Default Events
ASP.NET objects usually expose an event that is designated
as the default event.
In addition to a default event, many ASP.NET objects also
expose other events, called non-default events.

of 19
Non-default event handlers are used to respond to the non-
default events.
Each event has a specific signature associated with it.
Non-Default Event Handlers

of 19
Event wire-ups determine the procedures that need to be
called when objects raise events.
The AutoEventWireUp property of the .aspx pages should
be set to true to indicate that procedures with well-defined
names and signatures are used as event handlers.
By default, the AutoEventWireUp property of the .aspx
pages is set to true.
<%@ Page Language=“C#” AutoEventWireup=“True”%>
Event Wire-Ups

of 19
Centralized event handlers run in response to multiple events.
This helps in creating code that is easier to maintain.
Centralized Event Handlers

of 19
How to Determine Which Web Server Control Raised an Event
To determine which control caused the event, you need to
perform the following steps:
In the event handler, declare a variable with a type that
matches the control that raised the event.
Assign the sender argument of the event handler to the
variable, casting it to the appropriate type.
Examine the ID property of the variable to determine which
object raised the event.

of 19
When a Web browser makes a request for a Web page, it
sends information that describes the browser in the Hypertext
Transfer Protocol (HTTP) header.
You can query the information sent by the browser by using
code in the ASP.NET Web page.
Detecting the browser capability ensures that the response
the application sends to the browser is appropriate.
Much of the information sent by the Web browser is
encapsulated as properties in the Request.Browser object.
Browser Capability Detection

of 19
The header section of the HTML script contains metadata for
the page such as title and styles used in the page.
The metadata is useful in search engines for categorizing the
Web pages.
The information in the page header can be used at run time
by the server-side code.
The page header information can be changed at run time.
ASP.NET exposes each Web page to your code as a
System.Web.UI.Page object.
You can use the properties of the Page.Header object,
such as the Page.Header.Title property, to query and set
its values at run time.
Page Header Retrieval

of 19
How to Pass Values Between ASP.NET Web Pages
You can pass information between pages in various ways:
Use a query string that appends the information to the URL of
the target page
Expose the data as public properties on the source page

of 19
The HttpServerUtility.Transfer Method
The HttpServerUtility.Transfer method performs
the following functions:
Halts the code running on the current Web page
Requests a different Web page to carry on the processing
Example:
Server.Transfer("Productdisplay.aspx?productname=
bike&color=blue");

of 19
ASP.NET enables you to handle run time errors with:
Structured exception handling:
It enables you to handle exceptions in your Web applications by
using Try…Catch blocks.
Page-level error handling:
It enables you to trap all the otherwise-unhandled server-side
errors on the page.
Page_Error event of the Page object enables you to trap all the
unhandled exceptions in a page.
Application-level error handling:
It enables you to trap all the otherwise-unhandled server-side
errors in the Web application.
There are two standard approaches you can follow when
implementing an application-level error handler:
Create Application_Error event method in global.asax file
Include a <customErrors> element in the Web.config file
Page-Level and Application-Level Error Handling

of 19
Handling Application-Level Errors Using <customErrors> Element
Using the <customErrors> elements requires you to
modify the web.config file of your web application.
Refer to the following code snippet:
<system.web>
<customErrors
defaultRedirect="errorhandler.aspx“ mode="On">
<error statusCode="403”
redirect=“Page1.htm"/>
<error statusCode="404”
redirect=“Page2.htm" />
</customeErrors>
</system.web>

of 19
Problem Statement:
You are a developer in the Adventure Works organization, a
fictitious bicycle manufacturer. You have been asked to assist in
the development of the Business-to-Consumer (B2C) Web
application and a Business-to-Employee (B2E) extranet portal.
Decisions on the design of the application have already been
taken. You have been asked to carry out a number of specific
tasks in order to implement various elements of this design.
Demo: Programming a Web Application

of 19
As part of the first phase of the B2C development, you have
been asked to complete prototypes for the following pages:
• Feedback.aspx. You will create a centralized event handler for the
Click event of two Button objects.
• Contact.aspx. You will create an event handler for the non-default
Command event of Button objects.
• Diagnostics.aspx. You will retrieve properties of the Browser object
and display them on the Web page. You will also access the
Page.Header object.
• TrailReport.aspx. You will implement a page-level error handler
that deals with all run-time errors that can occur on this Web page.
You will also modify the Web.config file to enable application-
level error handling by redirecting all otherwise-unhandled
exceptions to the customErrors.aspx page.
Demo: Programming a Web Application (Contd.)

of 19
Solution:
To solve this problem, you need to perform the following tasks:
1. Implement Non-Default Event Handlers
a.Open the Adventure Works Web site.
b.Create a centralized event handler for two Button controls.
c. Specify the feedback_Click method as the Click event handler for
the feedback buttons.
d.Create an event handler for the Command event of Button controls.
e.Specify the SortGroup_Command method as the Command event
handler for the Button controls.
f. Test the Web site functionality.

of 19
2. Detect Browser Capabilities and Set Page Header Properties
a.Review the Diagnostics.aspx page.
b.Detect browser properties.
c. Display browser properties.
d.Modify the page title.
e.Test the Web site functionality.
3. Handle Page-Level Exceptions
a.Handle page-level exceptions.
b.Handle exceptions at the application level.
c. Test exception handling.

of 19
In this session, you learned that:
ASP.NET objects usually expose an event that is designated
as the default event.
In addition to the default event, ASP.NET objects expose other
additional events known as non-default events.
When you want to write code that responds to a non-default
event, you need to define an event handler for it.
Event wire-ups are the mechanism that ASP.NET uses to
determine which procedures to call when objects raise events.
By default, the AutoEventWireUp attribute for .aspx pages is
set to true.
When a Web browser makes a request for a Web page, it
sends information that describes the browser in the Hypertext
Transfer Protocol (HTTP) header.
Summary

of 19
Centralized event handlers run in response to multiple events.
ASP.NET provides a robust and flexible error-handling
framework. It enables you to handle run-time errors with:
Structured exception handling
Page-level error handlers
Application-level error handlers
Summary (Contd.)

02 asp.net session02

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (16)

Similar to 02 asp.net session02

Similar to 02 asp.net session02 (20)

More from Vivek chan

More from Vivek chan (17)

Recently uploaded

Recently uploaded (20)

02 asp.net session02