13 asp.net session19

Developing Web Applications Using ASP.NET
Objectives

In this session, you will learn to:
Describe the Page Scripting Object Model
Explain how to use tracing and instrumentation to monitor and
improve the performance of a Web application
Describe ASP.NET 2.0 caching techniques
Explain how asynchronous processing can lead to improved
performance for Web applications
Describe strategies for dealing with session state management
issues when deploying Web applications in a Web farm
environment
Access Page Scripting Object Model functionality
Implement tracing and instrumentation in Web applications
Implement ASP.NET 2.0 caching techniques

Ver. 1.0 Slide 1 of 27

The Page Scripting Object Model

ASP.NET is a server-side programming model.
Client side code can be useful to respond quickly to the
user action, if it can be completed without extra information
from the server.
To respond to a user action, the browser needs to post the
page back across the Internet for processing. This slows
down the application significantly.


The Page Scripting Object Model (Contd.)

• Client–side script can be added to an ASP.NET page by
using <script> tags, without the runat=“server”
attribute.
• Client-script generated by ASP.NET controls does not
interfere with any script added using <script> tag.
• You can also add client-side script to a page by using
server-side code.
• Creating client script in server code is useful when:
Contents of the client script depend on information that is not
available until run time.
The client script needs to be executed when the page finishes
loading.
The client script needs to be executed when users submit the
page.



An attribute added to an ASP.NET server control which is
not defined by their classes is processed by the browser.
This feature can be used to define client-side event
handlers for controls.
A server control can be referred in the client-side script by
using its ID property as set in the server-side code.
A server control can also be referred in the client-side script
by setting the ClientID property of the control.



Adding Client Scripts Dynamically:
• In case client-side script depends on information available only
at run time, it can be generated and added in the page at run
time by using the System.Web.UI.ClientScriptManager
class.
• To add client script to a page dynamically, you need to call one
of the following methods:
RegisterClientScriptBlock
RegisterClientScriptInclude
RegisterStartupScript
RegisterOnSubmitStatement



The following code adds a script that will execute in the
browser when the user attempts to submit a form:
void Page_Load ()
{
String scriptText = “return confirm(‘ Do you want
to submit the page?’)”;
ClientScript.RegisterOnSubmitStatement
(this.GetType(), “ConfirmSubmit”, scriptText);
}



Client Callbacks Without Postbacks:
Client callbacks provide a way to obtain information from the
server without executing the entire page again.
In a client callback, client-side code on the page invokes a
server-side method without performing a postback. This
method can return results back to the client-side script.
An ASP.NET page that implements client callback must:
Implement the ICallbackEventHandler interface.
Include a method that implements the RaiseCallbackEvent
method from the interface.
Contain the following client script functions:
A helper method that performs the callback
A method that receives the callback from the server code
A method that calls the helper method



Implementing the ICallbackEventHandler Interface:
A page can implement the ICallbackEventHandler
interface by defining the class for the page as:
public partial class CallBack_class:
System.Web.UI.ICallbackEventHandler
Implementing the RaiseCallbackEvent Method:
The following is a sample implementation of the
RaiseCallbackEvent method of the
ICallbackEventHandler interface:
public string RaiseCallbackEvent (string
eventArgument)
{
Return eventArgument + “ new value”;
}



Sending the Callback:
The following example shows how to dynamically create a
function that invokes the callback:
void Page_Load(object sender, EventArgs e)
{
string cbReference =
Page.ClientScript.GetCallbackEventReference(
this, “arg”, “ReceiveServerData”,
“context”);
string callbackScript = “function
CallTheServer(arg, context) {“ + cbReference
+ “; }”;

Page.ClientScript.RegisterClientScriptBlock(
this.GetType(), “CallTheServer”,
callbackScript, true);
Ver. 1.0
} Slide 9 of 27


The following example shows how an HTML input button
control can initiate the callback process:
<input type=“button” id=“MyButton”
onclick=“return CallTheServer(‘Some
Data’);” />



Receiving the Callback:
The following example shows how to create a client-side
method for receiving a callback:
<script type=“text/javascript”>
function ReceiveServerData(rvalue, context)
{
span1.innerText = “Return value = “ +
rvalue;
}
</script>


Tracing and Instrumentation in Web Applications

• Tracing features enable gathering of information for
debugging and performance tuning.
• Tracing can be enabled for an ASP.NET page by adding
trace=“true” attribute to the <%@page%> directive.
• Diagnostic information, mostly related to the performance of
the application is generated and displayed at the bottom of
the rendered page.
• Custom instrumentation data can be added to the trace
information displayed by calling methods on the
System.Web.TraceContext class.
• In addition to displaying messages that you send, trace
information includes the times at which the messages were
received. This can be used to diagnose parts of the code
that execute slowly.


Tracing and Instrumentation in Web Applications (Contd.)

• The classes in the System.Diagnostics namespace
allow you to implement a tracing system.
• Trace statements must be added at strategic points within
the code to generate tracing information.
• Trace Listener objects receive tracing output and write it to
logs, text files, or the screen.
• ASP.NET tracing information can also be sent to a
System.Diagnostic listener by using Web.config file:
<system.web>
<trace writeToDiagnosticsTrace=“true”/>
<CustomErrors mode=“off”/>
</system.web>


Tracing and Instrumentation in Web Applications (Contd.)

• The System.Diagnostics tracing information can be
routed to the browser by the using Web.config file:
<system.diagnostics>
<trace>
<listeners>
<add name = “WebPageTraceListener”
type=“System.Web.WebPageTraceListener,
System.Web,
Version =2.0.3600.0,
Culture=neutral,
PublicKeyToken=b03f5f7f11d50a3a”/>
</listeners>
</trace>
</system.diagnostics>


ASP.NET 2.0 Caching Techniques

• Objects and pages that require substantial resources can
be cached for reuse.
• The application cache enables caching of objects and data
for reuse.
• Storing data in the application cache is similar to storing
data in the Application object.
• Objects in the cache are volatile and can be removed
without warning.
• Another type of cache, the Page Output cache stores
rendered pages in server memory.
• You can enable Page Output caching by including the
<$@ OutputCache %> directive on the page:
<%@ OutputCache Duration=“60”
VaryByParam=“None”%>


ASP.NET 2.0 Caching Techniques (Contd.)

• In some cases, it is not feasible to cache the entire page.
• A page can be cached partially by:
• Adding <%@OutputCache%> directive in the control that needs
to be cached.
• Placing <%@OutputCache%> directive on the page and
marking certain sections exempt from caching by surrounding
these sections with a Substitution control.
• Multiple versions of a page can be cached by using
varybyparam attribute in the <%@OutputCache%>
directive:
<%@OutputCache Duration = “60” VaryByParam=“City”%>


Asynchronous Processing in Web Applications

• A Web page can be configured to execute some requests
asynchronously.
• On a Web page, it can be specified that runtime should not
necessarily wait for a long method to complete before
continuing with the next piece of code.
• The Async property of the Page object is used to enable
code on a Web page to run asynchronously:
<%@ page Async=“true”%>
To perform an asynchronous operation, the following
methods need to be registered:
• Begin: This method sets the operation running.
• End: This method responds when the operation has
completed.


Asynchronous Processing in Web Applications (Contd.)

Calling Web Services Asynchronously:
Web services can be hosted on servers remote from the one
that hosts the Web application.
Web services can be called asynchronously in case other
operations do not depend on their result.
There are two ways to call a Web service asynchronously:
By using a callback
By using a WaitHandle
Loading XML Asynchronously:
XML files can be large and located remotely from the Web
server. As a result, they may take a long time to load.
XML files can be loaded asynchronously in the same way as a
Web service.


ASP.NET Performance Counters

Are used to capture performance data and log them in the
Performance Logging database or Windows Performance
monitor.
ASP.NET supports the following types of performance
counters:
System: Are exposed in the Windows Performance monitor as
the ASP.NET performance counter object.
Application: Are exposed as the ASP.NET Applications
performance object.
The following are some of the performance counters:
Anonymous Requests
Transactions Pending
Requests Timed Out


Web Farm Development Considerations

Response time of a Web application can be reduced by
hosting it on a Web farm.
A Web farm is group of servers configured to act as a single
Web server.
The servers in a Web farm can share the processing
between them.
You should consider using a Web farm if you have
optimized your application fully and upgraded your server
as much as possible but the application is still not
responding quickly.


Web Farm Development Considerations (Contd.)

Considerations for Building a Web Farm:
Using an External Session State Provider:
In a Web farm each request in a session can be directed to different
servers in the farm. Therefore, it is not practical to store session
state in memory of any of the servers.
Two external session state providers can be used:
The ASP.NET State Service
Microsoft SQL Server
Configuring the <MachineKey> tag in machine.config:
• The <machineKey> tag configures the way encryption is used to
protect forms authentication cookies and view state information.
• Encryption keys are generated automatically and are unique to
each server.
• To access shared protected information in a Web farm, each server
must use the same encryption keys.


Web Farm Development Considerations (Contd.)

Deploying to a Web Farm:
Each server in a Web farm must have an identical copy of the
application.
Microsoft Windows Installer package is helpful to ensure
consistency among different servers while deploying the
application.


Demo: Optimizing Web Application Performance

Problem Statement:
You are a developer in the Adventure Works organization, a
fictitious bicycle manufacturer You have been asked to assist
in creating a new Business-to-Consumer (B2C) Web
application and a related Business-to-Employee (B2E) extranet
portal.
Decisions on the design of the application have already been
made. You have been asked to carry out a number of specific
tasks in order to implement various elements of this design. As
part of the first phase of the B2C development, you have been
asked to prototype various performance related techniques for
the Web application.


Demo: Optimizing Web Application Performance (Contd.)

Solution:
• You need to perform following tasks:
1. Access the Page Scripting Object Model
• Open the starter solution.
• Write the test code to set the focus to the Name text box when
displaying the Online Survey page.
• Use the ClientScript object to inject client-side script that displays
a message box onto the Web page.
• Use the ClientScript object to implement out-of-band callbacks.
• Add a client-side JavaScript function for receiving the result of the
callback.
• Test the callbacks.


Demo: Optimizing Web Application Performance (Contd.)

1. Implement ASP.NET Caching Techniques
• Implement page caching declaratively.
• Implement parameterized page caching in code.
• Prevent portions of a page from being cached by using a
Substitution control.
• Implement Web page fragment caching by using a Web user control.
2. Implement Tracing and Instrumentation Techniques in Web
Applications
a. Add and review tracing information on a Web page.
b. Add event logging capabilities to the Web application.
c. Add and manipulate performance counters for the Web application.
d. Test the logging and performance counter management of the Web
application.


Summary

In this session, you learned that:
• Client-side script can be added to an ASP.NET page by using
<script> tags, without the runat=“server” attribute.
• System.Web.UI.ClientScriptManager class is used to
generate and render client-side code at run time.
• To enable tracing for an ASP.NET page trace=“true”
attribute can be added to the <%@Page%> directive.
• The classes in the System.Diagnostics namespace also
provides a tracing system.
• The ASP.NET application cache enables the storing of objects
and data for reuse.
• A page can be cached by including the <%@OutputCache%>
directive on the page.


Summary (Contd.)

• The Async property of the Page object enables code on the
Web page to run asynchronously.
• Response time of a Web application can be improved by
hosting it on a Web farm.
• The ASP.NET State Service or Microsoft SQL Server can be
used as an external session state provider in a Web farm.


13 asp.net session19

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