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Introduction to Web Forms and Web Controls

Fundamentals of Web Forms

Introduction

To make it possible to create an interactive web page that allows visitors to provide values that a webserver can process, APS.NET, from the .NET Framework, provides various types of classes. To start, you must create a form and add it to a webpage.

To support forms, the .NET Framework provides a class named HtmlForm . It is indeed the .NET's implementation of the HTML's form element that is used to create a form.

Creating a Web Form

As it is done in HTML, to get a form on a webpage, create a <form> element. Here is an example that starts a form:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<title></title>
</head>
<body>

<form></form>

</body>
</html>

HTML Elements in a Webform

The form element is a container in which you can put any type of HTML element. Here is an example that contains a p and a div elements:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head>
<title>Geometry: Square</title>
<style type="text/css">

#formulation
{
    margin: auto;
    width:  200pt;
}
#main-title
{
    font-size:   18pt;
    font-weight: bold;
    font-family: Georgia, "Times New Roman", Times, serif;
}
</style>

</head>
<body>

<form>
  <div id="formulation">
    <p id="main-title">Geometry: Square</p>
  </div>
</form>

</body>
</html>

You can also include scripting code, from code delimiters, in a form element. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head>
<title>Geometry: Square</title>
<style type="text/css">

#formulation
{
    margin: auto;
    width:  200pt;
}
#main-title
{
    font-size:   18pt;
    font-weight: bold;
    font-family: Georgia, "Times New Roman", Times, serif;
}
</style>

</head>
<body>

<form>
  <div id="formulation">
    <p id="main-title">Geometry: Square</p>

    <% Response.Write("<p>A square is a flat geometric figure made of four equal sides and four right angles.</p>") %>
  </div>
</form>

</body>
</html>

This would produce:

Fundamentals of Web Forms

 
 
 

The Method Used to Send Data

Introduction

When the user clicks a button used to collect information from a webpage, it is assumed that the information on the form is sent to the server. HTML allows you to specify how this information would be sent. To support this, the <form> tag is equipped with an attribute named method. This attribute can be assigned one of two values: get or post.

Getting the Data

In the <form> tag, you can add the method attribute and assign the get (or GET, this is not case-sensitive) value to it. Here is an example:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<title>Geometry: Square</title>
</head>
<body>

<form method="get" runat="server">

</form>

</body>
</html>

If you do this, the information that is being sent would display in the address bar, starting with a question mark. Here is an example:

Method = GET

Notice that, in the address bar, after the address of the web page, there is a question mark, followed by various words. If you use GET as the method to send data, the information being carried should not exceed 2048 characters (if we consider that each character uses a byte).

Posting the Data

An alternative is to assign post (or POST) to the method attribute. This would be done as follows:

<form method="post" runat="server">

</form>

In this case, the information is sent directly to the server through a protocol (in this case, HTTP) and would not appear in the address bar of the browser. If you use POST as the method to send data, the information being carried can be as large as the user/visitor's computer memory (RAM) can afford.

Taking Action

Once the information from a form reaches the server, it must be processed. This is usually done by specifying the file that includes the code used to process the information that was sent. A regular file in this case would have the .aspx extension. This can be the same file that contains the form or it can be a separate file.

To specify the file used to process information from a form, the <form> tag is equipped with an attribute named action to which you can assign the name of the file, as a string. This can be done as follows:

<form method="post" action="index.aspx" runat="server">

</form>

As with all HTML attributes, the position of the ACTION attribute is not important. That is, it can be positioned before or after another attribute.

Web Controls Fundamentals

Introduction to Web Controls

To have a meaningful interactive webpage, its form must be equipped with objects named web controls. To support those controls, the .NET Framework provides various classes, each for a particular goal.

Creating a Web Control

As opposed to classic HTML Web controls, ASP.NET Web controls use a special formula for their tags. A tag starts with <asp: followed by the name of the class that represents the control. For example, if a class for a control is named Something, its start tag would be <asp:Something>. As it is normally done in HTML, the element must be closed with an ending tag. For a control named Something, this would be</asp:Something>. Therefore, the creation of a control could start as follows:

<asp:Something></asp:Something>

An alternative in closing a control tag is to end the start tag with a forward slash and omit the end tag. This can be done as follows:

<asp:Something />

Client and Server Processing

When creating an ASP.NET control for your web page, you must specify where its value(s) would be processed. This is done by adding the Runat (or runat) attribute to the start tag of the web control. It can have one of two values: client or server, which would be assigned to the attribute. Here is an example:

<asp:Something runat="server"></asp:Something>

This attribute and its value must be applied to every ASP.NET Web control, including the form. The attribute should also be added to various types of elements, including the head. Here are examples:

<%@ Page Language="VB" %>

<!DOCTYPE html>

<html>
<head runat="server">
<title>Geometry: Square</title>
<style type="text/css">

#formulation
{
    margin: auto;
    width:  200pt;
}
#main-title
{
    font-size:   18pt;
    font-weight: bold;
    font-family: Georgia, "Times New Roman", Times, serif;
}
</style>

</head>
<body>

<form runat="server">
<div id="frmSquare">
    <p id="main-title">Geometry: Square</p>

    <% Response.Write("<p>A square is a flat geometric figure made of four equal sides and four right angles.</p>") %>

</div>
</form>

</body>
</html>

This would produce:

A Control for Input

Identifying a Web Control

To be able to identify a control in your code, you should (must) give it an HTML identification. This is done by adding the id attribute to the start tag of the control and assigning it a name as a string.

 
 
   
 

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