ASP.net Session 13

7/30/2019 ASP.net Session 13

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Developing Web Applications Using ASP.NET

In this session, you will learn to:

Handle and log errors

Debug Web applications

Implement Web parts in a Web application

Objectives


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It is possible that certain unexpected errors occur in a Web

application while it is running in a real-world environment.

It would be easy to resolve such errors if a log of these

errors is maintained.

ASP.NET enables you to log unhandled errors in an eventlog, database, or some other file.

To log errors occurring in an application, you need to create

a log for the application in the event log.

Whenever an unhandled error occurs in a Web application,

the Application_Error event handler written in theGlobal.asax file is executed.

Logging Errors


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A log can be created by using the EventLog class of the

.NET Framework.

The following table describes the various properties of theEventLog class.

Logging Errors (Contd.)

Proper ty Descr ipt ionEntries Used to retrieve the contents from an event log.

Log Used to specify the name of the log from where the log information is to

be read or written.

Source Used to specify the name by which the application needs to be

registered in the event log. The name specified as the Source property

should be unique in an event log. A single event log can contain content

from multiple sources.


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The following table describes the various methods of theEventLog class:

Logging Errors (Contd.)

Method Descr ipt ion

Exists Used to determine whether the log to which the information is to be

written or read exists on the specified computer. If the computer is not

specified, the existence of the log is checked on the local computer.

SourceExists Used to determine whether a particular source name already exists on

the specified computer. If the computer is not specified, the existence of

the event source is checked on the local computer.

CreateEventSourc

e

Used to establish an application as a valid event source for adding

information to a log.

WriteEntry Used to write information to an event log.


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Problem Statement:

When a user clicks the Add New Album Details button on the

AddAlbumDetails page, the application throws a default error.

As a developer, you need to ensure that a custom error page

is displayed whenever an error occurs on the

AddAlbumDetails page. In addition to displaying the customerror page, you need to log the error in a log file.

Activity 8.1: Implementing Page-Level Error Handling


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Solution:

To display a custom error page and to log the error in a log

file, you need to perform the following steps:

1. Modify the Global.asax file.

2. Add a new Web page.

3. Design the new Web page.

4. Modify the web.config file.

5. Modify the AddAlbumDetails.aspx file

6. Execute the application.

7. Verify the logged error.

Activity 8.1: Implementing Page-Level Error Handling(Contd.)


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Debugging is the process of finding and fixing errors in an

application.

An application may contain syntax errors, logical errors, and

run-time errors. The syntax errors are resolved during the

compilation of the Web application.The logical errors and run-time errors cannot be caught

during compilation. Such errors require you to debug the

code while it is running.

Debugging Web Applications




There are various tools available that help you debug your

Web application.

One such tool is Visual Debugger available in Visual Studio

IDE.

The debugging tools enable you to step line-by-line throughthe statements in an application to ensure that the execution

path and the data are correct.

Debugging Web Applications (Contd.)




To enable debugging in your ASP.NET Web application, you

must configure the application to compile into a debug build.

You can configure a Web application to compile into a

debug build by setting the debug attribute in the

element of the web.config file to

true, as

shown in the following code snippet:

Configuring Web Applications for Debugging


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You can attach a debugger to client-side scripts.

Client-side debugging works only with Internet Explorer.

Debugging Client-Side Scripts

Let us see how to debug client-side scripts


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A Web part:

Is a modular unit that can contain any type of Web-based

information, which could be a picture, static text, or database

information.

Enables a user to create a personalized user interface and

enables you to present information in a better way.

Enables you make your websites interactive.

Implementing Web Parts in a Web Application


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The advantages of using Web parts in a website are:

Web parts enable users to personalize the content of a Web

page.

Web parts can be assigned role-based access, thereby,

determining which Web part can be shared by all users or

which should be hidden for certain roles.

Web parts can be connected to each other. One of the

connected Web parts is defined as a provider and the other as

a consumer.

Advantages of Using Web Parts


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Personalization is one of the main advantages of using Web

parts.

You can implement personalization by allowing a user to

view a Web page in several display modes.

Display modes allow users to modify or personalize theWeb page.

The different types of display modes available are:

Browse

Edit

DesignCatalog

Connect

Web Part Modes


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ASP.NET provides you with the Web parts control set that is

designed to implement Web parts in your websites.

Some of the Web part controls available in ASP.NET are

described in the following table.

Web Parts Control Set

Property Descript ion

WebPartManager Manages all the Web part controls on a page. Each Web

part page contains exactly one WebPartManager control.

CatalogZone Contains CatalogPart controls and is used to create a

catalog of Web part controls from which a user can select

a Web part control to add to a page.

EditorZone Contains EditorPart controls and is used to enable a user

to edit and personalize Web part controls on a page.

WebPartZone Contains the overall layout for the Web Part controls that

compose the main user interface of a page.ConnectionsZone Contains Connection controls.

CatalogPart Contains a list of available Web part controls that a user

can add to a page.

Connection Creates a connection between two Web part controls on a

page.

EditorPart Serves as the base class for specialized controls that

provide the functionality to edit Web parts.


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Once you have created a Web part page, you can allow

users to switch between the various Web part display

modes.

To enable a user to switch between the various modes, you

can include a drop-down list on the Web page that allows a

user to select the desired mode.

Web Parts Control Set (Contd.)


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You can then type the following code snippet in the

SelectedIndexChanged event of the DropDownList control:WebPartManager wpm =

WebPartManager.GetCurrentWebPartManager(Page);

string selectedMode = DropDownList1.SelectedValue;

WebPartDisplayMode mode =

wpm.SupportedDisplayModes[selectedMode];

if (mode != null)

{

wpm.DisplayMode = mode;

}

Web Parts Control Set (Contd.)


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Problem Statement:

The management of MusicMania wants its website to provide a

customizable user interface to all its users. The users should be

able to hide, show, and arrange the components on the home

page according to their requirements.

As the first step towards implementing this requirement, youneed to create a Web parts page, Portal.aspx. The Portal.aspx

page should include a Web part that displays the availability

status of the MusicMania database.

Prerequisite: Ask your faculty to provide you the required

starter files.

Activity 9.1: Creating a Web Parts Page


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Solution:

To create the Web parts page, you need to perform the

following tasks:

1. Create a user control.

2. Add a new Web page.

3. Design the new Web page.

4. Test the application.

Activity 9.1: Creating Web Parts Page(Contd.)


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There are situations where you need to connect sets of data

from different data sources.

Web part connections are based on a pull model, where the

consumer pulls data from the provider.

To create a connection, the provider control defines acommunication contract in the form of an interface, indicating

the data it can provide.

The consumer control knows about this contract and retrieves

the data through the connection.

Connecting Web Parts


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To participate in a connection, a Web part needs to define a

connection point.

Connection points are of two types:

Provider connection points

Consumer connection points

Connecting Web Parts (Contd.)


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To create connected Web parts, you need to perform the

following tasks:

1. Create the provider Web part as a custom control.

2. Create the consumer Web part as a custom control

3. Add the Web parts to the Toolbox.

4. Add the Web part controls from the Toolbox to a Web part page

and assign an ID and title to each of the two controls.

5. Add the connection information to the WebPartManager control

by opening the Web part page in the Source view and adding a element inside the

element.

Connecting Web Parts (Contd.)

Let us see how to create and use a Web user control


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In this session, you learned that:

ASP.NET enables you to log unhandled errors in an event log,

database, or some other file.

An event log can be created by using the EventLog class of the

.NET Framework.

Debugging is the process of finding and fixing errors in an

application.

There are various tools available that help you debug your

Web application. One such tool is Visual Debugger available in

Visual Studio IDE.

The features of a debugger that help you debug Webapplications are:

Breakpoints

Stepping

Data Viewing

Summary


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The aspnet_wp.exe process is attached to the debugger to

debug a running page.

A Web part is a modular unit that can contain any type of Web-

based information.

The advantages of using Web parts in a website are:

Web parts enable users to personalize the content of a Webpage.

Web parts can be assigned role-based access, thereby

determining which Web parts can be shared by all users or which

should be hidden for certain roles.

Web parts can be connected to each other.

The different types of display modes of a Web part are:

Browse mode

Edit mode

Design mode

Catalog mode

Connect mode

Summary (Contd.)


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A Web page that is composed of Web parts is known as a Web

part page.

A Web part page is divided into zones that provide the

structure for placing Web parts.

Summary (Contd.)

Documents

ASP.net Session 13