Introduction
ASP.NET controls are the
heart of the ASP.NET Framework. An ASP.NET control is a .NET class that executes
on the server and renders certain content to the browser.
The ASP.NET Framework 2.0
contains over 70 controls. These controls can be divided into eight groups as
given below:
-
Standard Controls:
The standard controls enable us to render standard form elements such as
buttons, input fields, and labels.
-
Validation Controls:
The validation controls enable us to validate form data before you submit
the data to the server. For example, we can use a RequiredFieldValidator
control to check whether a user entered a value for a required input field.
-
Rich Controls:
The rich controls enable us to render things such as calendars, file upload
buttons, rotating banner advertisements, and multi-step wizards.
-
Data Controls:
The data controls enable us to work with data such as database data. For
example, you can use these controls to submit new records to a database
table or display a list of database records.
-
Navigation Controls:
The navigation controls enable us to display standard navigation elements
such as menus, tree views, and bread crumb trails.
-
Login Controls:
The login controls enable us to display login, change password, and
registration forms.
-
Web Part Controls:
The Web Part controls enable us to build personalizable portal applications.
-
HTML Controls:
The HTML controls enable us to convert any HTML tag into a server-side
control.
With the exception of the
HTML controls, we declare and use all the ASP.NET controls in a page in exactly
the same way. For example, if we want to display a text input field in a page,
then you can declare a TextBox control like this:
<asp:TextBox
id="TextBox1"
runat="Server"
/>
This control declaration
looks like the declaration for an HTML tag. Remember, however, unlike an HTML
tag, a control is a .NET class that executes on the server and not in the web
browser. When the TextBox control is rendered to the browser, it renders the
following content:
<input
name="TextBox1"
type="text"
id="Text1"
/>
The first part of the
control declaration, the asp: prefix, indicates the namespace for the control.
All the standard ASP.NET controls are contained in the System.Web.UI.WebControls
namespace. The prefix asp: represents this namespace. Next, the declaration
contains the name of the control being declared. In this case, a TextBox control
is being declared. This declaration also includes an ID attribute. We use the ID
to refer to the control in the page within our code. Every control must have a
unique ID. It is good practice to use ID attribute to every control even when we
don't need to program against it. If we don't provide an ID attribute, then
certain features of the ASP.NET Framework won't work. The declaration also
includes a runat="Server" attribute. This attribute marks the tag as
representing a server-side control. If we neglect to include this attribute,
then the TextBox tag would be passed, without being executed, to the browser.
The browser would simply ignore the tag. Finally, notice that the tag ends with
a forward slash. The forward slash is shorthand for creating a closing </asp:TextBox>
tag.
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