asp.net session 02

7/30/2019 ASP.net Session 02

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Developing Web Applications Using ASP.NET

In this session, you will learn to:

Implement server controls

Objectives


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In the earlier days of Web development, the programmers

had to use HTML controls to design a Web application.

The HTML controls do not provide any built-in methods and

events.

Programmers had to manually write the methods andevents using client-side scripts to create a dynamic Web

page.

This is very time consuming. In addition, it is insecure

because the client-side scripts are visible to users when

they view the source for the Web page.ASP.NET solves the problems associated with the use of

HTML controls by providing server controls.

Implementing Server Controls


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Server controls:

Are the fundamental building blocks that are specifically

designed to work with Web forms in an ASP.NET application.

Can be rendered as markup text on a Web browser.

Are capable of executing the program logic on the server.Provide built-in methods and events eliminating the need for

writing the events and methods manually.

Provide security to the application by hiding the program logic

from the user.

Provide an object-oriented programmable interface.

Can be viewed as special HTML tags, which are processed by

the server.

Implementing Server Controls (Contd.)


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Advantages of using server controls are:

Automatic state maintenance

Browser independent rendering

Easily programmable model

Implementing Server Controls (Contd.)


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When a page is requested for the first time, the server

controls are processed in the following sequence:

1. Initializing

2. Loading

3. PreRendering4. Saving

5. Rendering

6. Disposing

7. Unloading

Processing of Server Controls on a Web Page


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When the Web page is posted back to the Web server, the

server controls are processed in the following sequence:

1. Initializing

2. Loading view state

3. Loading control instance4. Loading the postback data

5. PreRendering

6. Saving

7. Rendering

8. Disposing9. Unloading

Processing of Server Controls on a Web Page (Contd.)


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ASP.NET provides the following types of server controls:

HTML server controls

Web server controls

Validation controls

Types of Server Controls




HTML server controls:

Are processed by the Web server.

Make full use of the .NET Framework utilities such as

validation.

The following table lists some of the common HTML servercontrols with their description.

Types of Server Controls (Contd.)

HTML Server Controls Description

HtmlAnchor control Works as the HTML tag but runs on the server. It is used to

direct the user from one page to another.

HtmlInputText

control

Works as the HTML tag but runs on the

server. It is used to gather information from the user.

HtmlInputCheckBoxcontrol

Works as the HTML tag but runs onthe server. It is useful to implement questions that can have onlytwo answers, such as yes/no or true/false

HtmlInputRadioButton

control

Works as the HTML tag but runs on the

server. You can use the HtmlInputRadioButton control to implementmultiple-choice questions, where a user can select only one option.

HtmlSelect control Works as the HTML element but it runs on the server. It

is used to create a list box and when a user has to select an option

from a list of options.




Web server controls:

Are created on the server and require a runat=server

attribute to work.

Some of the most commonly used Web server controls are:

TextBox controlLabel control

ListBox control

CheckBox and CheckBoxList control

RadioButton and RadioButtonList control

AdRotator controlCalendar control

DropDownList control

ImageButton control



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ImageButton control

Button control

Wizard control

MultiView control

HyperLink controlFileUpload control

XML control

Substitution control



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Validation controls:

Are used for validating the values entered by the users in other

controls.

ASP.NET provides the following validation controls that can

be attached to input controls to validate the values that areentered by the user:

RequiredFieldValidator control

RegularExpressionValidator control

CompareValidator control

RangeValidator controlValidationSummary control

CustomValidator control



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ASP.NET server control event model:

In ASP.NET, events associated with the server controls

originate on the client but the processing of the events

happens only on the server.

ASP.NET supports the following two types of events:

Postback events: In postback events, a Web page is sent back to

the server for processing.

Nonpostback events: In nonpostback events, a Web page does

not immediately cause a postback.

Server Control Events


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Event handlers:

When an event is raised, the corresponding event handler is

searched and the code written in the event handler is

executed.

The various approaches that can be used to work with event

handlers include:

Using default events.

Using non-default events.

Using the AutoEventWireup capabilities of a Web form.

Creating centralized event-handlers.

Server Control Events (Contd.)


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Using default events:

A default event is an event that is most commonly associated

with a control.

Default events are handled by a default event handler.


Let us see how to create a default event handler


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Using non-default events:

In addition to the default event, each control exposes other

events, called non-default events.

Non-default events are handled by non-default event handlers.


Let us see how to create a non-default event handler


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Using the AutoEventWireup capabilities of a Web form:

ASP.NET provides the event wire-up capability to a Web form

using which events can be automatically associated with event-

handling procedures having well-defined names and

signatures.

Event wire-ups determine the procedures that need to becalled when objects raise events.

To enable the event wire-up capability of a Web form, you

need to set the AutoEventWireUp attribute of the .aspx page

to true.

By default, the AutoEventWireUp attribute of the .aspxpages is set to true, as shown in the following code snippet:



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The AutoEventWireup attribute can have the following two

values:

True: This means that the ASP.NET runtime does not require

events to specify event handlers, such as Page_Load and

Page_Init.

False: This means that the events need to specify event handlersexplicitly.



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Creating centralized event-handlers:

A centralized event handler eliminates the need for declaring

separate event handlers for different ASP.NET objects.

You can create one centralized event handler that can perform

appropriate action at runtime.

When you create a single event handler to respond to multiple

events that should trigger different actions, you need to

determine which event invoked the event handler by:

Declaring a variable in the event handler with a type that matches

the control that raised the event.

Assigning the sender argument of the event handler to thevariable, casting it to the appropriate type.

Examining the ID property of the variable to determine which

object raised the event.



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Two controls that act as containers when adding controls

dynamically are:

PlaceHolder: Is used as a container that is not visible in a Web

application. It reserves a place in the structure of the Web

page for other controls that are added dynamically

Panel: Renders div tag around all the child controls in the

panel, which makes it useful when you want to apply a css

class to a container.

Loading Controls Dynamically (Contd.)


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An event handler for a control is usually created at design

time.

It can also be created dynamically at run time for the

controls that are created dynamically.

Adding Event Handlers Dynamically


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Problem Statement:

MusicMania is a music store with its branches located all over

the United States. It has a huge collection of music albums to

cater to the tastes of all kind of music lovers. To increase the

sales, the management at MusicMania has decided to hire a

team of professionals to develop a Web application for sellingmusic online.

You, being a part of the team, have been asked to create a

file-system Web application. Initially, you are required to

design the Home page and the About Us page.

Activity 2.1: Creating a Web Application in ASP.NET


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Solution:

To design the home page of the MusicMania Web application,

you need to perform the following tasks:

1. Design the Home page.

2. Design the About Us page.

3. Execute the application.

Activity 2.1: Creating a Web Application in ASP.NET (Contd.)


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A generic handler can be used when you want to display

the contents of a text file, an XML file, or an image.

The generic handler provides a class that implements the

IHttpHandler interface.

The class provides the ProcessRequest method and theIsReusable property.

The ProcessRequest method is responsible for

processing individual HTTP requests.

The IsReusable property specifies whether the

IHttpHandlerFactory object can put the handler in apool and reuse it to increase performance.

The IHttpHandlerFactory object is the object that calls

the appropriate handler.

Implementing Generic Handler

Let us see how to create a generic handler


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In this session, you learned that:

Server controls are the fundamental building blocks that are

specifically designed to work with Web forms in an ASP.NET

application.

Server controls provide:

Automatic state maintenance.

Browser independent rendering.

Easily programmable model.

Summary


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The sequence in which a server control is processed when the

page is requested for the first time is:

1. Initializing

2. Loading

3. PreRendering

4. Saving5. Rendering

6. Disposing

7. Unloading

Summary (Contd.)


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The sequence in which a server control is processed when the

Web page is posted back to the Web browser is:

1. Initializing

2. Loading view state

3. Loading control instance

4. Loading the postback data5. PreRendering

6. Saving

7. Rendering

8. Disposing

9. Unloading

Summary (Contd.)


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The various types of server controls provided by ASP.NET can

be classified into the following categories:

HTML server controls

Web server controls

Validation controls

User controls

An event is a message that contains details about the user

action, such as the cause of the event and the control on which

the event occurred.

The two arguments passed by all events in ASP.NET are:

Sender objectEvent object

The two types of events in ASP.NET server control event

model are:

Postback events

Nonpostback events

Summary (Contd.)


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The two controls that act as container when adding controls

dynamically are:

PlaceHolder

Panel

Summary (Contd.)

asp.net session 02

Documents