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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